cos2x等于多少

cos2x 等于多少cos2x=cos2x-sin2x=2cos2x-1=1-2sin2x=(1-tan2x)/(1+tan2x)，即cos2x=1-2sinx 的平方。相关公式cos2x=cos2x-sin2x=2cos2x-1=1-2sin2x=(1-tan2x)/(1+tan2x)，即 cos2x=1-2sinx 的平方。相关公式cos3a=cos(2a+a)=cos2acosa-sin^2asina=(2cos^2a-1)cosa-2(1-cos^2a)cosa=4cos^3a-3cosasin2α=[1-cos(2α)]/2cos2α=[1+cos(2α)]/2tan2α=[1-cos(2α)]/[1+cos(2α)]