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Area of Triangles with Geoboards

Area of a triangle= 1/2 bh

If you are a kid that formula can look like gibberish.

Let’s use geoboards to help that formula make sense!

The area of this square is 16.  I can count those squares and that makes perfect sense.

Now I’m cutting the square in half and making a triangle.

What’s the area of that triangle?  Half of 16 = 8

Booyah!  I understand that.


1/2 of 4 X 4 = 8


1/2 of b x h

Let’s try this again:

I’m cutting up another triangle.  Let’s find the area of that blue one.

Logic tells me that the blue triangle is half of the green one.  The green triangle = 8.  So the blue trianle should equal 4, right?

Let’s proove it!

If I use my imagination I can flip half of the triangle over and it becomes a complete square.  Now I can “see” that the area of the blue triangle is four.

Or I can use the formula:

1/2 of b x h = 1/2 (4 x 2) = 4

Pretty cool, hunh?