证明cos^4A=1/4+cos2A+1/4cos^2A

问题描述:

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