Question

cos2x公式cos2x=1-2sinx^2cos2x=2cosx^2-1这公式是怎样推导出来的?

Answer 1

cos2x=cos^2 x-sin^2 x=cos^2 x-sin^2 x+1-1

=cos^2 x-sin^2 x+cos^2 x+sin^2 x -1

=1-2sinx^2=2cosx^2-1