Question:
In ∆ABC, ∠A = 40° and ∠B = 60°. Then the longest side of ∆ABC is
(a) BC
(b) AC
(c) AB
(d) cannot be determined
Solution:
(c) AB
In triangle $\mathrm{ABC}$, we have:
$\angle A=40^{\circ}, \angle B=60^{\circ} \quad \ldots$ (Given)
Here, $\angle A+\angle B+\angle C=180^{\circ}$
$\Rightarrow 60^{\circ}+40^{\circ}+\angle C=180^{\circ}$
$\Rightarrow \angle C=80^{\circ}$
$\therefore$ The side opposite to $\angle C$, i.e., $\mathrm{AB}$, is the longest side of triangle $\mathrm{ABC}$.