Question

if cos(a+b) =0, then sin (a-b) can be reduced to​

Answer 1

$\large\bf{As\:cos(a+b)}$

$\rightarrow$ $a+b=$ $cos^{-1}(0)=90°$

$\rightarrow$$a=(90-b)°$

$\rightarrow$$sin(a-b) = sin(90-b-b) = sin(90-2b) = cos2b$

$\Rightarrow$$sin(a-b)=cos(2b)$