Question

Упростите выражение:sin(π+a) *ctg(π-a) /cos(π/2-a)

Answer 1

$\displaystyle\bf\\\frac{Sin\Big(\pi+ \alpha\Big)\cdot Ctg\Big(\pi- \alpha \Big) }{Cos\Big(\dfrac{\pi }{2}-\alpha \Big) } =\frac{-Sin\alpha \cdot \Big(-Ctg\alpha \Big)}{Sin\alpha } =Ctg\alpha$