已知f=[sin(π-α)cos(2π-α)tan(-π-α)]/sin(-π-α),⑴化简f(a)、⑵若α是第三象限,且cos﹙α－3π/2

题目

已知f=[sin(π-α)cos(2π-α)tan(-π-α)]/sin(-π-α),⑴化简f(a)、⑵若α是第三象限,且cos﹙α－3π/2
且cos﹙α－3π/2﹚=1/5,求f（a）的值、⑶若α＝﹣1860°,求f(a)的值
⑴-sinα ⑵ 1/5 ⑶根号3/2
我要具体步骤.

答案

⑴f(α) = [sin(π-α)cos(2π-α)tan(-π-α)]/sin(-π-α)= [sin(α)cos(-α)tan(-α)]/sin(α)= cos(-α)tan(-α)= cos(-α) * sin(-α) / cos(-α)= sin(-α)= -sin(α)⑵cos﹙α - 3π/2﹚=cos﹙-2π + π/2 + ...