证明cos^4A=1/4+cos2A+1/4cos^2A

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证明cos^4A=1/4+cos2A+1/4cos^2A证明cos^4A=1/4+cos2A+1/4cos^2A证明cos^4A=1/4+cos2A+1/4cos^2A(cosA)^4=[(cosA)

证明cos^4A=1/4+cos2A+1/4cos^2A
证明cos^4A=1/4+cos2A+1/4cos^2A

证明cos^4A=1/4+cos2A+1/4cos^2A
(cosA)^4=[(cosA)^2}^2=[(1+cos2A)/2]^2
=1/4+cos2A+(cos2A)^2 得证