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If S is a point on side PQ of a triangle PQR such that PS = QS = RS, then

(A)PR .QR = RS^{2}         (B)QS^{2} + RS^{2} = QR^{2}

(C) PR^{2} + QR^{2} = PQ^{2}    (D) PS^{2} + RS^{2} = PR^{2}

Answers (1)

Answer : [C]

Given: In triangle PQR

PS = QS = RS

\Rightarrow PS = RS

\therefore \angle 1=\angle 2 ...(1)

(Q If a right angle triangle have equal length of base and height then their acute angles are also equal)

\text{Similarly} \angle 3=\angle 4 ...(2)

( Q corresponding angles of equal sides are equal)

\text{In }\Delta PQR

\angle P+\angle Q+\angle R=180^{o}             

\because sum of angles of a triangle is 180°

\angle 2+\angle 4+\angle 1+\angle 3=180^{o} ....(3)

Using equation (1) and (2) in (3) 

\angle 1+\angle 3+\angle 1+\angle 3=180

2\left ( \angle 1+\angle 3 \right )=180^{o}

\Rightarrow \angle R=90^{o}

\text{Here }\angle R=90^{o}\therefore \Delta PQR \text{is right angle triangle }

PR^{2} + QR^{2} = PQ^{2}

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