分子
=sin^2 (x+π/4)
=[1-cos(2x+π/2)]/2
=[1+sin(2x)]/2
=(sin²x+2sinxcosx+cos²x)/2
=(sinx+cosx)²/2
分母
=2cos^2 x+sin2x
=2cos^2 x+2sinxcosx
=2cosx(sinx+cosx)
原式
=分子/分母
=(tanx+1)/4
又tan(π/4-x)=-1/3
tan(x-π/4)=1/3
tanx=(1/3+1)/(1-1/3)=2
原式=3/4
满意请轻戳此处
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