In triangle PQR, PQ = 1cm, QR = 2cm and PQR = 120o Find the…

In triangle PQR, PQ = 1cm, QR = 2cm and PQR = 120^o Find the longest side of the triangle

Correct Answer: Option B

Explanation

PR² = PQ² + QR² – 2(QR)(PQ) COS 120^o
PR² = 1² + 2² – 2(1)(2) x – cos 60^o
= 5 – 2(1)(2) x -(frac{1}{2})
= 5 + 2 = 7
PR = (sqrt{7})cm