Question

sin(a+b)-sin(a-b)/cos(a+b)-cos(a-b)=-ctga

Answer 1

$frac{sinacosb+cosasinb-sinacosb+cosasinb}{cosacosb-sinasinb-cosacosb-sinasinb}=-ctga frac{2cosasinb}{-2sinasinb}=-ctga -ctga=-ctga$