KS3

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

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

Area of triangle

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WHAT YOU NEED: two pieces of paper/card, pencil, scissors, ruler.
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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.
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STEP 2: Use the scissors to cut along the line. You should be left with two duplicate triangles.
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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.
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STEP 4: Move the smaller triangles to either side of the larger triangle. You should be left with a rectangle.
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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.

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