Question

i see cosx= -sinx and somewhere cosx= +sin x which one is correct

Answer 1

cos (90+x) or cos(270-x) = -sinx

cos(90-x) or cos(270+x) = +sinx

never cosx=-sinx or cosx=+sinx this is wrong neve cosx will be equal to +/- sinx

but when cos45=sin45 like this cases it may happen and according to the condition i said above

hope it helps