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


`A C^{2}=A B^{2}+B C^{2}`


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

Construction:- Construct a triangle P Q R right angled at Q such that, P Q=A B

and {QR}={BC}

Proof:-

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