根据下列条件求函数 f(x)=sin(x+π/4)+2sin(x-π/4)-4cos2x+3cos(x+3π/4) 的值：（1）x=π/4（2）x=3π/4
问题描述：
根据下列条件求函数 f(x)=sin(x+π/4)+2sin(x-π/4)-4cos2x+3cos(x+3π/4) 的值：（1）x=π/4（2）x=3π/4
答
(1)f(x)=sin(π/4+π/4)+2sin(π/4-π/4)-4cosπ/2+3cos(π/4+3π/4)=sin(π/2)+2sin0-4*0+3cosπ
=1+0-4*0+3*(-1)=-2
(2)把x=3π/4代入,得f(x)=0+2-4*0+3*0=2