Question

If $\Delta$ $ABC$ is right angled at $C$, then the value of $\cos (A+B)$ is:

• A. $0$
• B. $1$
• C. $\frac{1}{2}$
• D. $\frac{\sqrt{3}}{2}$

Answer 1

The correct option is A $0$

If $C={90}^0$
Therefore
$\cos (A+B)$
$=\cos ({180}^0-C)$
$=\cos ({180}^0-{90}^0)$
$=\cos \left({90}^0\right)$
$=0$