What makes a shape its shape
Learning to look past how a shape usually looks, to what actually makes it a triangle, is your child's first taste of careful reasoning in geometry. In 2nd grade they name shapes by their sides and corners, and in 3rd grade they sort shapes into families, such as seeing that a square is also a rectangle. Children who rely on looks alone often miss a triangle that is turned on its side.
In this video, your child will learn to tell what makes a shape its shape.
The lesson stops at each question for your child's answer.
Three problems, each a little harder
Each problem is worked step by step. Your child will solve the last one before Bobby shows how.
Example 1
What makes a shape a triangle?
Example 2
Which one is not a triangle?
Your child's turn
Which one is not a rectangle?
The two key steps
- 1Count the straight sides, and check it is closed.
- 2Color, size and turn don't change a shape.
Mistakes to listen for
- Rejecting a triangle that is upside down or long and thin, because it does not look like the usual pointing-up picture.
- Calling a square tilted on one corner a diamond, and therefore not a square, because it has been turned.
- Accepting a shape with a gap or a curved side as a triangle because it has three corners.
The lesson shows every step, so your child sees why it works. Read our parent's guide to what makes a triangle a triangle →
Is your child ready to practice what they've learned?
Bobby's Math Club offers unlimited practice for free.
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More 1st grade Geometry, with questions your child answers along the way.
Questions parents ask
Does my child need an account to watch?
No. You can watch this on any device at any time. If your child would like to practice what makes a triangle a triangle, and you'd like parent-friendly reports on your child's progress and growth, you can join Bobby's Math Club for unlimited free practice.
What happens when my child answers a question?
A right answer gets a cheer, and the lesson carries on. If your child isn't sure, they can tap "I don't know yet", and Bobby gives the answer and shows another example. Nothing is scored or stored.
Is this the same lesson that's on YouTube?
Yes. Here, the lesson stops at each question and waits for your child to answer. On YouTube, each question stays on screen for a few seconds, and then the lesson plays on.
Where can I learn more?
There's a short, kid-friendly lesson like this one for every Pre-K to 5th grade math skill, all in our video library. Our parent's guide to what makes a triangle a triangle has more on where kids get stuck and how you can help at home. In the club, your child practices at just the right level, about five minutes a day, and you get parent-friendly reports as they grow. Learn more about how it works →
Practice what makes a triangle a triangle
Questions at your child's level, about five minutes a day, on what makes a triangle a triangle and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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