Question

In ΔABC, a = 7cm, b = 3cm and c = 8 cm, then angle A is ______ 

Options

• `pi/6`

• `pi/4`

• `pi/3`

• `pi/2`

Answer 1

In ΔABC, a = 7cm, b = 3cm and c = 8 cm, then angle A is `underline(pi/3)`.

Explanation:

cos A = `(b^2 + c^2 - a^2)/(2bc) = (9 + 64 - 49)/(2 xx 3 xx 8) = 1/2`

⇒ A = `cos^-1(1/2) = pi/3`