How to show the area of a triangle is ½ × base × height

This video can not be played

To play this video you need to enable JavaScript in your browser.

A short video showing how to show the area of a triangle is half base × height.

Image caption,
Click to see a step-by-step slideshow.
Image caption,
WHAT YOU NEED: two pieces of paper/card, pencil, scissors, ruler.
Image caption,
STEP 1: Place one piece of card on top of the other and use the ruler to draw a line from the bottom left corner of the card to any point on the top edge. Draw a line from that point to the other corner to make a triangle.
Image caption,
STEP 2: Use the scissors to cut along the line. You should be left with two duplicate triangles.
Image caption,
STEP 3: Take one of the triangles and use the ruler to fold a vertical line down the middle. Cut along the fold. You should now be left with two smaller triangles and one larger triangle.
Image caption,
STEP 4: Move the smaller triangles to either side of the larger triangle. You should be left with a rectangle.
Image caption,
You’ve done it! The areas of the two identical triangles form a rectangle with the same base and height as the triangle. The area of this rectangle is base × height. So you've shown the area of the triangle is half this rectangle = ½ base × height.

Discover more about this topic from Bitesize.