Question

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

Answer 1

Given, $\Delta ABC$ is right-angled at $C$ then $C={90}^o$ and $A+B={90}^o$.

Then,

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