cos2x=cos^2x-sin^2xsin^2x=(1-cos2x)/2cos^2x=(cos2x+1)/2y=1+sin^2x =1+(1-cos2x)/2,T=pi,max=2,min=1;y=2sinx-3cosx=(2^2+3^2)^(1/2)*sin(x-arctan(3/2)) T=2*pi;max=(13)^(0.5).min=-（13)^(0.5).y=cos^2x-cos^4...