In △ PQR, right angled at Q, PR + QR = 25 cm and PQ = 5 cm. Determine the value of cos R.
1213
Applying Pythagoras Theorem
PR2 = PQ2 + QR2
⇒ (25−QR)2 = 52 + QR2
i.e.,(QR−25)2 = 52 + QR2
⇒ QR2−50QR+625=25+QR2
⇒ 50QR=600
⇒ QR=12 cm
Therefore,
PR=25−12=13 cm
So,
cosR=QRPR=1213