In triangle PQR, PQ = 1cm, QR = 2cm and PQR = 120o Find the longest side of the triangle
- \(\sqrt{3}\)cm
-
\(\sqrt{7}\)cm
- 3cm
- 7cm
The correct answer is: B
Explanation
PR2 = PQ2 + QR2 - 2(QR)(PQ) COS 120oPR2 = 12 + 22 - 2(1)(2) x - cos 60o
= 5 - 2(1)(2) x -\(\frac{1}{2}\)
= 5 + 2 = 7
PR = \(\sqrt{7}\)cm