化简cos^4(a/2)-sin^4(a/2)

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化简cos^4(a/2)-sin^4(a/2)化简cos^4(a/2)-sin^4(a/2)化简cos^4(a/2)-sin^4(a/2)[cos(a/2)]^4-[sin(a/2)]^4={[cos

化简cos^4(a/2)-sin^4(a/2)
化简cos^4(a/2)-sin^4(a/2)

化简cos^4(a/2)-sin^4(a/2)
[cos(a/2)]^4-[sin(a/2)]^4
={[cos(a/2)]^2+[sin(a/2)]^2}×{[cos(a/2)]^2-[sin(a/2)]^2}
=1×{[cos(a/2)]^2-[sin(a/2)]^2}
=cos[2×(a/2)]
=cosa