Theorem 6.9 : In a triangle, if square of one side is equal to the sum of the squares of the other two sides, then the angle opposite the first side is a right angle.

Explanation

Given:- `A B C` is a triangle


{AC}^{2}={AB}^{2}+{BC}^{2}


To prove:- `\angle B=90^{\circ}`


Construction:- Construct a triangle `P {QR}` right angled at `{Q}` such that, `{PQ}={AB}` and `{QR}={BC}`


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