1.已知tanX=2,求:(tan2X—tanX)/(1+tan2X tanX)的值.

问题描述:

1.已知tanX=2,求:(tan2X—tanX)/(1+tan2X tanX)的值.
2.化简:sin(X—Y)cosY+cos(X—Y)sinY
3.cos80°sin50°—sin40°sin80°=?
4.若X,Y为锐角,且sinX=(12/13),sinY=(3/5),则sin(X+Y)的值为?
5.计算(1)sin15°cos15° ;(2)2(cos^2 )* (π/8) —1
6.已知cosX=(1/5),(3π/2)

(tan2X—tanX)/(1+tan2X tanX)=tan(2X—X)=tanX=2sin(X—Y)cosY+cos(X—Y)sinY=sin(X—Y+Y)=sinXcos80°sin50°—sin40°sin80°=cos80°(sin90°-40°)—sin40°sin80°=cos80°cos40°—sin80°sin40°=cos(80°+...