Question

Can some explain me this step

Answer 1

$\cos(\pi - 2h) \: goes \: to \: the \: 2nd \: quadrant \: \\and \: in \: 2nd \: quadrant.... \: the \: value \: for \: cos \: \alpha \: is \: negative \: \\ so \: we \: took \: negtative \: sign$


Hope it helps...