zhangzhengni
幼苗
共回答了24个问题采纳率:83.3% 举报
分子=4(cosx)^4-2(2cos²x-1)-1
=4(cosx)^4-4cos²x+1
=(2cos²x-1)²
=cos²2x
sin²(π/4-x)
=cos²[π/2-(π/4-x)]
=cos²(π/4+x)
所以分母=[sin(π/4+x)/cos(π/4+x)]*cos²(π/4+x)]
=sin(π/4+x)cos(π/4+x)
=1/2*sin[2(π/4+x)]
=1/2*sin(π/2+2x)
=1/2*cos2x
所以f(x)=2cos²2x/cos2x=2cos2x
所以f(-17π/12)
=2cos(-17π/6)
=2cos(7π/6)
=2cos(π+π/6)
=-2cos(π/6)
=-√3
1年前
10