Question

For a acute $△ABC$, the value of $\frac{\cos (A+B)}{\cos C}$ is

• A. $0$
• B. $-1$
• C. $1$
• D. $\cot (A+B)$

Answer 1

The correct option is B $-1$

$A+B+C=\pi \Rightarrow A+B=\pi -C$

Now,
$\frac{\cos (A+B)}{\cos C}=\frac{\cos (\pi -C)}{\cos C}=-1$