Question

In ∆ ABC, ∠B = 90°, AB = 3 cm and AC = 6 cm.
Then, ∠A = ?
(a) 30°
(b) 60°
(c) 45°
(d) None of these
Figure

Answer 1

(b) 60^o

In right-angled ∆ ABC, we have:
$$\begin{gathered} \cos A=\frac{AB}{AC}=\frac{3}{6}=\frac{1}{2}=\cos {60}^{\mathrm{o}} \\ \therefore A={60}^{\mathrm{o}} \end{gathered}$$