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

显示全部楼层 · 2011-7-22 17:55:23

且cos﹙α－3π/2﹚=1/5,求f（a）的值、⑶若α＝﹣1860°，求f(a)的值
答案：⑴-sinα ⑵ 1/5 ⑶根号3/2
我要具体步骤。。。

千问 · 2011-7-22 17:55:23

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 + α ﹚= cos(π/2 + α) = -sin(α) =1/5∴ f(α) = -sin(α) = 1/5⑶f(α) = -sin(α) = -sin(-1860°) = -sin(-5×360°- 6...

千问 · 2011-7-22 17:55:23

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) *tan(-α)
= sin(-α)
= ...