求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2
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求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2求证：cosa(
求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2
求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2
求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2
原式=cos^2a-cosa*cosb+sin^2a-sinasinb
=1-cosa*cosb-sina*sinb
=1-[cos(a+b)+cos(a-b)]/2-[cos(a-b)-cos(a+b)]/2
= 1-cos(a-b)
=1-[1-2sin^2(a-b)/2]
=2sina^2(a-b)/2
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求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2
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