Question

计算：cos(70°+α)sin(170°-α)-sin(70°+α)cos(10°+α)

要详细过程，急需答案！

Answer 1

sin x = sin (180° - x)
所以，
sin (170° - a) = sin [180° - (170° - a)]
= sin (10° + a)

根据方程式，
sin(u ±v) = sin u cos v ± cos u sin v

sin (10° + a) cos (70° + a) - cos (10° + a) sin (70° + a)
= sin [(10° + a) - (70° + a)]
= sin - 60°
= - sin 60°
= -(√3)/2
= -0.866

纯手打，蒙采纳，谢谢~~