因为cos(2x)=cos^2(x)-sin^2(x)且cos^2(x)+sin^2(x)=1则sin^2(x)=1-cos^2(x)则cos(2x)=2cos^2(x）-1 则2cos^2x=1+cos2x y=2cos^2x+sin2x=cos2x +sin2x+1=[2^(1/2)]cos(2x-45)+1其中[2^(1/2)]等于根号2...