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

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

### Question

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

### Options

A) $$\sqrt{3}$$cm

B) $$\sqrt{7}$$cm

C) 3cm

D) 7cm

### Explanation:

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

## Dicussion (1)

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