Question

IN $△ABC$ right angled at $C$, find the value of $\cos (A+B)$.

Answer 1

In Fig.

$\because \angle C={90}^o$

$\therefore \angle A+\angle B={90}^o$ (By angle sum property)

Hence, $\cos (A+B)=\cos \left({90}^o\right)=0$