How to prove Pythagoras' theorem

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A one-minute video showing you how to prove Pythagoras' theorem: that the area of the square on the longest side of a right-angled triangle is equal to the sum of the squares on the other two sides.

How to prove Pythagoras' Theorem

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WHAT YOU NEED: Paper, pencil, scissors and a ruler.
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STEP 1 - RIGHT TRIANGLE x 4: Take one piece of card and fold it in half, then fold it in half again...
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... use the ruler and pencil to draw a straight line across the bottom corner of the folded card. It will work best if it’s a fairly steep angle...
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... use the scissors to cut along the line. You should now be left with four identical right-angled triangles.
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STEP 2 - MAKE SQUARE, CUT OUT: Place the triangles on the other piece of card. Arrange with their right angles outwards, so they form the outline of a square. Draw a dot at each outside corner of the square...
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...join the dots with a ruler and pencil, and then use the scissors to cut along the lines - you should be left with a square.
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STEP 3 - SQUARE IN MIDDLE: Arrange the triangles on the square so there's one in each corner. Slide the bottom left triangle up towards the right until it meets the triangle top right. Slide the top left and bottom right triangles together in the bottom left corner.
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STEP 4 - TWO SMALLER SQUARES: You should now see two smaller yellow squares. If you look at the triangle that was originally in the bottom left corner, each of its sides is now the side of one of the smaller yellow squares.
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As the total yellow area has remained the same, the area of the yellow square on the longest side MUST be the same as the squares on the other two sides. You have created a visual proof of Pythagoras' theorem!