化简1/2sin2a-cos^2(π/4-a)

问题描述:

化简1/2sin2a-cos^2(π/4-a)

cos^2(π/4-a)=(1/2)*[2cos^2(π/4-a)-1]+1/2=(1/2)*cos(π/2-2a)+1/2=(1/2)*sin2a+1/2 所以原式=(1/2)*sin2a-(1/2)*sin2a-1/2=-1/2