A shape is symmetric when both sides are identical, and the line of symmetry is the fold line that divides the shape into two matching halves; by folding a shape along its line of symmetry and cutting, you can create two identical shapes from one original shape.
Deep Dive
Prerequisite Knowledge
- No data available.
Where to go next
- No data available.
Deep Dive
Monster Cake Mistake | Learning Math for Kids! | Monster Math SquadAdded:
Monster cake mistake.
Hey Goo, what you making? It's a paper airplane, Monster Max. See? I just take this triangle and fold it in half like this. And see?
A PAPER >> [screaming] >> AIRPLANE MONSTER. It flies really well.
I notice.
And the scream screen always surprises Goo. The scream screen.
Somewhere in Monsterville there's a monster in need. And whenever a monster needs our care THE MONSTER MATH SQUAD WILL BE THERE.
It's Miss Merkly. She makes monster muffins and cakes in her muffin shop.
Hi, Miss Merkly. Hi, Monster Math Squad.
I've made a big cake mistake. What happened, Miss Merkly? The monster twins placed an order today.
>> You mean Even Stevie and Even Evie? Yes, but I made a mistake that has completely ruined everything. Can you help? The Monster Math Squad is on the way.
Hmm, we need to help Miss Merkly fix the big mistake she made with the monster twins cake order.
I bet we can use monster math for that.
YEAH, MONSTER MATH can do anything.
Because monster math is everywhere. Hey, will you join the Monster Math Squad on the job? Join the squad. Join the squad.
You will? Awesome. First, we need the secret monster math word that will help us get THE JOB DONE.
>> [screaming] >> WORD MONSTER.
TODAY'S SECRET monster math word is symmetric.
Next time you see Word Monster and hear him squawk, shout out the secret monster math word with us to make something math amazing happen. Symmetric!
Not yet, Goo. Wait until you see Word Monster again.
Waiting's hard. Come on, Monster Math Squad. Let's go help Miss Merkle fix her big cake mistake.
Thank goodness you're here, Monster Math Squad. Huh? Are those your famous CRUSTY CARROT CAKES? YES. I was about to decorate them when I realized my mistake. I love the fun shapes you're baking them in. The shapes are the problem. Why? Listen to the order and you'll see. Dear Miss Merkle, please bake us crusty carrot cakes in different shapes. But that's what you did.
Yes, and then I realized it's Even Stevie and Even Evie who want them.
Everything for them has to be exactly the same. WHAT'S THE PROBLEM? THERE ARE TWO for Even Stevie and two for Even Evie. THAT'S EVEN. THAT'S THE SAME.
But do they look the same?
What do you think, Squad?
No, none of these cakes are the same shape. And that means the twins won't want any of them. Why don't you just make another set of four cakes just like these and the twins will be happy? I can't make any more cakes. I've used up all my ingredients. That is a problem.
How are we going to get two sets of cake shapes that are the same out of THESE FOUR CAKES?
>> [screaming] >> DID YOU SEE WORD MONSTER?
That means we all need to SHOUT THE SECRET MATH WORD, SYMMETRIC. Are you ready? LET'S SHOUT IT TOGETHER ON THREE.
1 2 3 SYMMETRIC LOOK, IT WORKED. A monster math monitor.
This snow monster has two weeds she wants to decorate the same, but the paper circles are all different. That's the way they came.
How can she make two matching sets? She has a great trick. It's easy because you see, circles are symmetric.
She folds a circle down the middle very carefully. The line the fold [music] makes is called the line of symmetry.
Then she tears the circle on the line and what do you know?
>> [music] >> She's got two matching ornaments all ready to go.
When a shape is symmetric, both sides are the same in every way. So when all the circles are folded and torn, the sets match. Hooray!
Thanks monster math monitor.
Now we know all about symmetric. If you have a symmetric shape like a circle, you can get two new identical shapes out of it. And since symmetric is a math word, let's do monster math.
>> [screaming] >> I see a circle. Great. If we cut it down its line of symmetry, we'll have a set of two matching cakes. How do we find its line of symmetry? We can't fold a cake down the middle like the paper circles the monster math monitor showed us. No, you certainly can't. But, I never make a cake without giving it a matching paper doily. Maybe you can use that somehow? Thanks Ms. Merkle.
If we fold the paper doily in half, right down the middle, we'll find its line of symmetry.
Here it goes. I fold it in half. I open it up. And there's the line of symmetry with both sides the same on each side of the line. Just place the doily on the cake, and I'll cut along the line of symmetry.
>> [groaning] >> NOW, WE'VE GOT A SET of two matching cakes. Perfect for even Stevie and even Evie.
Uh, too bad the rest of the cakes aren't circles. This one's a heart shape. Maybe it's symmetric, too. Will you help us check?
Monster Math Riffic.
Okay, I take the doily, fold it in half, open it up.
A perfect line of symmetry.
Are both sides the same?
They are. That means A heart shape is a symmetric shape.
Place the doily on the cake, Lily, and I'll cut along the line of symmetry.
Wow, now we've got another set of matching cakes for even Stevie and even Evie.
What about this one? What shape is it?
A triangle. Let's see if it's a symmetric shape.
Hmm, I can't figure out where the line of symmetry is on this doily. The shapes on each side of this line are definitely not the same. Does that mean this triangle shape is not symmetric? Oh, what do WE DO NOW?
>> [screaming] >> DID YOU SEE, WORD MONSTER?
THEN let's shout the secret monster math word, symmetric. Together again on three. Ready?
1 2 3 SYMMETRIC!
LOOK, A MONSTER math monitor.
The snow monster wants to hang paper moons on both her weeds [music] to make them look pretty. But she only has one moon. She needs to find the line of symmetry.
She tries to fold it in half, but that looks lame. It isn't symmetric. The sides don't look the same.
The snow monster wonders, on closer inspection, if maybe the line of symmetry runs in another direction.
Not up and down, but maybe across the middle.
This shape is symmetric. [music] She has solved the moon-shaped riddle.
Thanks, math monitor. Now we know that some shapes have a line of symmetry that runs down the middle. And some shapes have a line of symmetry that runs across them. Let's try folding this triangle across the middle and see what happens.
Is it symmetric? Are the sides the same now?
Yes, it worked. Okay, Max, put it on the cake and I'll cut it.
Another set of matching shapes.
Now for this one.
Nope, that's not symmetric. I'll fold it the other way.
Nope, the two sides still aren't the same. It doesn't work for the L shape. I guess that means that some shapes aren't symmetric. If it's not symmetric, we can't use it. Oh, we've got to hurry and get these decorated. Even Stevie and Even Evie will BE HERE SOON.
WOW, these crusty carrot cakes are perfect. Thanks, Miss Merky. We'll take them all. Except that one. Since we can't both have one of those. It wouldn't BE EVEN.
YEAH!
GO AHEAD. YOU MONSTERS deserve a massive monster treat. Uh, the pieces aren't the same. One piece is bigger than the other. I should have the biggest piece, Goo, because I'm the biggest monster. I should have the biggest piece, Max, because I'm the the greenest monster. Yeah.
I know what to do.
Oh, Lilly!
This looks symmetric. There. Now your pieces are the same.
Monster-math-errific job, Monster Math Squad. We helped Miss Merky fix her mistake with the monster twins' cake order, and we did it by knowing all about symmetric. That deserves a great big monster howl on three. ONE, TWO, THREE.
>> [screaming] >> WE DID THE MATH. WE DID THE MONSTER MATH.
CAKE TIME!
>> [laughter] >> JOKE MONSTER MACHINE.
OKAY, GOO. What shapes can you make?
Well, I'll show you, Max. TRIANGLE, CIRCLE, SQUARE.
>> [screaming] >> WHAT SHAPE ARE YOU NOW, GOO?
SQUISHED.
The scream screen always surprises Goo.
The scream screen.
Somewhere in Monstervia, there's a monster in need. And whenever a monster needs our care, THE MONSTER MATH SQUAD WILL BE THERE.
It's Joke Monster. He always plays jokes on monsters.
It's fun. HI, JOKE MONSTER. UH JOKE MONSTER, NO, I'm not Joke Monster.
You're not?
>> [laughter] >> I'M JUST JOKING.
OF COURSE I'M JOKE MONSTER.
>> [laughter] >> Good joke, Joke Monster. What can we do for you? Well, Lily, I just got a Joke Monster machine. What's a Joke Monster machine? Oh, you'll see. [laughter] It's so much fun. Is it behind that big box?
No, Max. It's not behind the box. It's in the box. Yeah, that's [laughter] the problem. I can't get the box open. Can you help me, Monster Math Squad? You bet we can. The Monster Math Squad is on the way. Please hurry. I can't wait to see my new Joke Monster machine in action.
We need to help Joke Monster open that box so he can get his Joke Monster machine out.
I'm sure we can use Monster Math to do that. Yeah, Monster Math can do anything. Because Monster Math is everywhere. Hey, will you join the Monster Math Squad on the job? Join the squad. Join the squad. You will?
Awesome. First, we need the secret Monster Math word that will help us get THE JOB DONE.
WORD MONSTER.
TODAY'S secret Monster Math word is fit.
Next time you see Word Monster and hear him squawk, shout out the secret Monster Math word with us to make something math-amazing happen. Fit.
>> [laughter] >> Not yet, Goo. Wait until you see Word Monster again. Oh, >> [laughter] >> right, Lily. Come on, squad. Let's go help open that Joke Monster Machine box.
HI, JOKE MONSTER. OH, EXCELLENT. It's the Monster Mask Squad here to help me.
Let me shake your hand.
I played another JOKE ON YOU.
>> [laughter] >> IT'S my hand shake buzzer.
Isn't it fun? Fun?
Uh, yeah.
Maybe you should try it, Max. Um, thanks, Scoob, but I think watching you was enough fun for me. Wow, that really is a big box. OH, YEAH.
IT IS A BIG, BIG BOX. IT IS BIG. And inside is my Joke MONSTER MACHINE, BUT I CAN'T get it open.
How have you tried to open the box, Joke Monster? I've pushed, pulled, tugged. I EVEN TRIED TO RIP IT OPEN. Nothing worked.
Hey, look. I found another box. Oh, and there's something in it.
Three triangle shapes. I wonder what those are for.
Oh, hold on. Did you say triangle shapes? Look.
There's a triangle cut out of the side of the box. Hmm, maybe we can open the box by putting the proper triangle shaped piece into this cutout. Ooh, like a key. Good idea, Lily. Let's give it a try.
Oh, it doesn't seem to fit.
What What think? Is this triangle the right size?
No, it's way too big.
What about this triangle? Is it the right size?
No, it's way too small.
The first triangle was too big and the second triangle was too small. Maybe this triangle IS THE RIGHT SIZE.
HMM, does that triangle look like it's the right size?
Yes, it does look like it's the same size so it must be the right piece.
Let's see if it fits. What do you think squad? Does it fit?
No. We tried all three triangle shapes and none of them fit the cutout in the box. Oh, what do WE DO NOW?
>> [screaming] >> DID YOU SEE WORD MONSTER?
That means we all need to shout THE SECRET MONSTER MATH WORD, FIT. Are you ready? LET'S SHOUT IT TOGETHER ON THREE.
ONE, TWO, THREE. FIT.
LOOK, it worked. A monster math monitor.
A monster is visiting an art gallery.
What an interesting piece of art. But wait, it seems to be missing a part. A triangle-shaped piece is what needs to be found.
Oh, there it is, right there on the ground.
It doesn't fit, but that can't be.
This triangle-shaped piece is the right size, you see.
The monster takes the piece and turns it around. That did the trick. The missing piece has been found.
Thanks math monitor, that was monster math-errific.
I think the math monitor is trying to tell us that if we turn this triangle piece around, it will fit in the cutout on the box. And since fit is a math word, LET'S DO MONSTER MATH.
>> [screaming] >> WILL IT FIT NOW?
NO? Then let's keep turning it.
How about now? Does it fit? Not yet.
Keep turning it, Goo.
What about now? DOES IT FIT?
YES! We did it! [screaming] Thanks, squad.
IT WORKED!
OH, there it is!
Isn't it amazing? My very own joke monster machine. A miniature me!
>> [laughter] >> I CAN'T WAIT TO SEE it work. Uh, what's it supposed to do? A joke monster machine is supposed to play jokes on you and make you laugh.
>> [laughter] >> THIS IS DEFINITELY NOT WORKING. HMM.
Maybe it's sleeping. I know. Maybe if I make some noise, IT'LL WAKE UP.
IT'S STILL NOT WORKING. LOOK, another cutout. Do you know what shape that is?
It's a triangle. And look, here's another little box with more shapes in it. Great. Are you thinking what I'm thinking?
Yes. Maybe one of those shapes will fit the cutout on the machine to get it to work. What kind of shapes are they, Goo?
They're this shape.
Does that piece fit the cutout?
No. That piece is a circle, and the cutout is a triangle.
Oh, maybe this one. It's a triangle.
They look a little different. I don't think this triangle shape The triangle shape is the same size, but it points a different way, just like before. Do you remember what we did the last time to make it fit?
Aha! Turn it around. Let's try that.
I'll turn [screaming] it.
NOPE. UH-UH.
NOT THIS WAY. Um yeah, I think you turned it all the way back to where it started. Lilly, did I turn it wrong? No, Goo. You turned it all the way around, but it still doesn't fit. The points of the triangle shape never matched the points of the cutout. I'm confused.
What do WE DO NOW?
>> [screaming] >> DID YOU SEE WORD MONSTER?
THEN let's shout the secret monster mask word, "fit", together again on three.
Ready?
One, two, THREE, FIT!
LOOK, A MONSTER mask It's Math Monitor.
A monster is visiting an art gallery.
This painting is missing a triangle, too.
Oh, there it is. Now what should he do?
It still doesn't fit when he turns it around, but it's the only triangle piece to be found.
Flip the shape over. Yes, that's it.
Now the triangle [music] piece is a perfect fit.
Thanks, Math Monitor. That was helpful.
Now we know that flipping a triangle shape over will make it point a different way. So maybe the Math Monitor is telling us we need to flip this triangle piece over to make it fit.
Flip the triangle piece over, just like me.
Great flipping, Joke Monster. Come on, squad. Let's flip the triangle piece over and see if it fits INTO THE CUTOUT.
THE JOKE MONSTER MACHINE IS MOVING. Oh goody. Now get ready for some joke monster MACHINE MAYHEM.
THANK YOU VERY MUCH.
>> [laughter] >> GOOD ONE JOKE MONSTER MACHINE. I couldn't have done it better myself.
>> [laughter] >> Monster matherrific job Monster Math Squad. We helped Joke Monster get his Joke Monster Machine working and we did it by knowing all about fit. That deserves a great big monster howl on three.
One, two, three.
>> [screaming] >> WE DID THE MATH.
WE DID THE MONSTER MATH.
DELIVERY MONSTER DOESN'T DELIVER.
Okay Goo, Simon says touch your head.
Easy.
All right Max, my turn. Simon says touch your ear. Then make me a slime sandwich with putrid peppers.
Wow, I didn't get all that. Can you go back a bit? Okay Max, I'll say it backwards.
Peppers, putrid, with, sandwich, SLIME.
[screaming] SIMON SAYS HELP me up. Don't you mean up me help?
And the scream screen always surprises Goo. The scream screen.
Somewhere in Monstropolis there's a monster in need and whenever a monster needs OUR CARE THE MONSTER MATH SQUAD WILL BE THERE.
It's Play All Day Monster. She loves to play with toys all day. Oh, I sure do, Monster Math Squad. How can we help you, Play All Day Monster? I'm supposed to be getting a new toy today, a monster dump truck. But, the delivery monster hasn't delivered it yet. He should have been here by now. That's not good. Can you help me find out where Delivery Monster is so I can get my monster dump truck?
I'm sure we can. The Monster Math Squad is on the way. Oh, boy, that's great.
Please hurry.
Hmm, we need to find out where Delivery Monster is with Play All Day Monster's new toy.
I'm sure we can use Monster Math to do that. Yeah, Monster Math can do anything. Because Monster Math is everywhere. Hey, will you join the Monster Math Squad on the job? Join the squad. Join the squad.
You will? Awesome. First, we need the secret monster math word that will help us get THE JOB DONE.
>> [screaming] >> WORD MONSTER. TODAY'S secret monster math word is backwards. Next time you see Word Monster and hear him squawk, shout out the secret monster math word with us to make something math-amazing happen. Backwards.
>> [laughter] >> Not yet, Goo. Wait until you see Word Monster again.
>> Oh, right. I forgot. Come on, Squad. Let's go help Play All Day Monster find Delivery Monster so she can play with her monster dump truck.
Monster Math Squad, thank you so much for coming. Delivery Monster was supposed to start his deliveries here at stop number one.
Well, I don't see him anywhere. Or my Monster Dump Truck. Where oh where could he be?
Hey, it's Smooth Moves Monster. He knows all the moves. Maybe he knows what moves we need to make to find the Delivery Monster.
How do monsters need to move? Listen to Smooth, get in the groove. Hop and skip that way until you arrive at the very last stop, stop number five. Delivery Monster's going backwards today. He's starting at the end and then going the wrong way. So, go to stop five at the end of the line. You'll have to hop and skip [music] fast to catch him on time.
Thanks, Smooth Moves Monster. Did you hear that, squad? We have to hop and skip to the end of the line to stop number five. That's where Delivery Monster is starting his route today.
We're at stop one now. Come on, squad.
Hop and skip with us and help us count the stops along the way.
Stop number two.
Stop number three.
Stop number four.
STOP NUMBER FIVE. OH BOY, OH BOY, OH BOY.
Where are Delivery Monster and my Monster Dump Truck? I see deliveries.
That means Delivery Monster was already here. But, I don't see my Monster Dump Truck. Smooth Moves Monster said Delivery Monster was starting his deliveries at the end of his route and then going backwards. So, that means we have to go backwards to catch up to him.
But, uh how do we go backwards from STOP NUMBER FIVE?
>> [screaming] >> DID YOU SEE WORD MONSTER?
That means we all need to shout THE SECRET MONSTER MATH WORD, BACKWARDS. ARE YOU READY? LET'S SHOUT IT TOGETHER, ON THREE.
ONE, TWO, THREE, BACKWARDS!
LOOK, IT WORKED! A MONSTER MATH MONITOR.
A little monster climbed some stairs, bouncing her ball high in the air. One, two, three, four, five. At the top, she has arrived. Oops, her ball is bouncing down. Where, oh, where can it be found?
Here's a clue, it's on number one stair.
Just count [music] backwards and you'll find it there. The little monster starts at number five stair, then counts backwards down from there.
Five, four, three, two, one.
Time for more ball bouncing fun.
Thanks, math monitor. That was monstrously helpful. Now we know how to count backwards from five. Yes! Five, four, three, two, one.
That was fun. I bet knowing how to count backwards will help us get back to stop number one. And get my monster dump truck. And since backwards is a math word, let's do >> Let's do monster math!
>> [screaming] >> Okay, squad. We're at stop number five, and we know Delivery Monster is going backwards. So, if we go back over the route we just followed to get here, counting backwards starting with five, >> we'll catch up to him. Let's do it. Come on, squad. Help us count backwards.
Five.
Four. Look, more deliveries. That means Delivery Monster was here, but he has moved on. And he didn't deliver the Monster Dump Truck at this stop.
>> Let's keep going backwards, squad.
Three. No dump truck.
Two. Still no dump truck.
One.
Here we are, back at STOP NUMBER ONE.
NO DELIVERIES HERE. And no Monster Dump Truck.
Huh? What's that?
HE FINALLY ARRIVED. DELIVERY MONSTER.
OH, UM, hi Monster Math Squad. Hi Play All Day Monster. Wh- What are you all doing here? We're looking for you. And a special delivery for me, a Monster Dump Truck. Um, I've got it right here. Sorry if I'm a little late. I get confused sometimes. I think I was a little backwards today.
>> [laughter] >> I THINK YOU'RE RIGHT.
MY MONSTER DUMP TRUCK.
I [laughter] LOVE IT.
OH, THANK you so much. Um, okay, everybody stand back.
I'm going to take off now.
Um, oh. Uh, is there a problem, Delivery Monster? You do seem kind of confused today. Oh me, oh my. I think I've forgotten how to do my takeoff countdown. What's a countdown? I count backwards from five all the way down to one. And when I get to one, I take off.
I can't take off without a countdown, but I've forgotten how to count backwards. I think I forgot how to count backwards, too.
Look, the Monster Math Monitor. He can remind us how to count backwards from five.
First, count forward. Let's count together, squad.
One, two, three, four, five.
Now, backwards.
Here goes.
Five, four, three, two, one.
Thanks, Monster Math Monitor. That was a monster math-errific reminder about counting backwards. Now we can help Delivery Monster do his countdown FROM FIVE TO ONE so he can take off.
Are you ready to count backwards, squad?
Great. Starting with five. READY?
FIVE, [screaming] FOUR, THREE, TWO, ONE.
>> [screaming] >> OH, THAT'S how you count backwards. I remember now. Stand back.
Five, four, three, two, one.
Got to get going. Lots of important deliveries to make.
Um if only I could remember where to go.
>> [laughter] >> Thanks and so long, MONSTER MATH SQUAD.
BYE, DELIVERY MONSTER.
HEY, GOO. Would you like to play with my monster dump truck, TOO? WOULD I? OH, THAT WOULD BE MONSTER MATH-ERRIFIC.
WOW!
>> [laughter] >> I DON'T THINK GOO IS PLAYING WITH THE TRUCK. I think the truck is playing with goo.
Good job, Monster Math Squad. We helped Play All Day Monster find Delivery Monster and get her Monster Dump Truck.
And we did it by knowing all about backwards. That deserves a great big monster howl on three.
One, two, three.
WE DID THE MATH.
WE DID THE MONSTER [screaming] MATH.
Related Videos
Escaping the Fog
LogicLemurGaming
760 views•2026-06-03
Olympiad Mathematics | Indian | Can You Solve This One?
PhilCoolMath
650 views•2026-06-03
A Brutal Radical Expression Made Easy! The Shortcut Changes Everything.
tamoshop
112 views•2026-06-02
V : jee main /advance class 11 mathematics : Binomial Theorem class-1 ( 29 may 2026 )
dcamclassesiitjeemainsadva9953
125 views•2026-05-29
Is This Pentomino Tileable?
3cycle
241 views•2026-05-30
This Sudoku Has Many Lines!!
CrackingTheCryptic
2K views•2026-05-29
Olympiad Mathematics | Indian Can You Solve This One?
PhilCoolMath
268 views•2026-06-02
Olympiad Mathematics | Indian | Can You Solve This?
PhilCoolMath
669 views•2026-06-02











