Correct Answer - Option 1 : 7
Given:
∠PQR = 135°
PQ = 8√2 cm
PR = 17 cm
Formula used:
Cosine rule - cosθ = (b2 + c2 – a2)/2bc
Calculation:
Let the value of b be x
According to the question
Cos 135° = [x2 + (8√2)2 – (17)2]/2 × x × 8√2
⇒ -1/√2 = (x2 + 128 – 289)/(2 × x × 8√2)
⇒ -1/√2 = (x2 – 161)/2 × x × 8√2
⇒ -16x = x2 – 161
⇒ x2 + 16x – 161 = 0
⇒ x2 + 23x – 7x – 161 = 0
⇒ x(x + 23) – 7(x + 23) = 0
⇒ (x + 23) (x – 7) = 0
⇒ x = -23, 7
∴ The required value of QR is 7