sin(α-π/2)cos(3π/2+α)tan(π-α)/tan(-α-π)sin(-π-α)
=-cosa*sina*(-tana) / (-tana)*sina
=-cosa
1)
f(a)=-cosa
2)
cos(α-3π/2)=-sina=1/5
α是第三象限角
sina=-1/5
cosa=-√(1-(-1/5)^2=-2√6/5
f(a)=-cosa=2√6/5
sin(α-π/2)cos(3π/2+α)tan(π-α)/tan(-α-π)sin(-π-α)
=-cosa*sina*(-tana) / (-tana)*sina
=-cosa
1)
f(a)=-cosa
2)
cos(α-3π/2)=-sina=1/5
α是第三象限角
sina=-1/5
cosa=-√(1-(-1/5)^2=-2√6/5
f(a)=-cosa=2√6/5