1、a是第三象限角,f(a)=sin(a-派/2)cos(3/2派+a)tan(派-a)
tan(-a-派)sin(-派-a)
（1）化简f(a)（2）若cos(a-3/2派)=1/5,求f(a)的值
f(a)=sin(a-π/2)cos(3π/2+a)tan(π-a)
tan(-a-π)sin(-π-a)
=[sin(π/2-a)][sin a][-tan a]
[-tan a][-sin(π+a)]
=[cos a][sin a][tan a][tan a]
[sin a]
=[tan a][sin a]^3
cos(a-3π/2)=1/5
cos(3π/2-a)=1/5
-sin a=1/5
f(a)=[tan a][sin a]^3
=[sin a]^4/cosa
=-[1/625]/[(2根6)/5
=-(根6)/1500