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Question

In PQR, right angled at Q, PR + QR = 25 cm and PQ = 5 cm. Determine the value of cos R.


A

1213

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B

513

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C

512

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D

1512

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Solution

The correct option is A

1213


Applying Pythagoras Theorem

PR2 = PQ2 + QR2

(25QR)2 = 52 + QR2
i.e.,(QR25)2 = 52 + QR2
QR250QR+625=25+QR2

50QR=600

QR=12 cm

Therefore,
PR=2512=13 cm

So,
cosR=QRPR=1213


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