Euclid Book 1 - Proposition 48
Inverse of Pythagoras' theorem

Index --- introduction --- definitions --- axioms and postulates --- propositions --- other

To be proved: If in a triangle the square on one of the sides equals the sum of the squares on the remaining two sides of the triangle, then the angle contained by the remaining two sides of the triangle is right.

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There is a triangle ABC with BC squared = BA squared + AC squared

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