# Theorem 15 - The Converse of Pythagoras' Theorem

This demonstrates that

**if**the square of the longest side is equal to the sum of the squares of the other two sides then the angle opposite the longest side**must be 90 degrees.**Drag the slider to change the size of the angle A.
Notice that

**only**when Pythagoras' theorem applies is the angle opposite the longest side**90 degrees.**## New Resources

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