函数cosx-sin平方x-cos2x+7/4的最大值是多少

是2y=cosx-(sinx)^2-(cosx)^2+(sinx)^2+7/4=-[(cosx)^2-cosx-7/4]=-[(cosx-1/2)^2-2]=2-(cosx-1/2)^2cosx属于[-1,1]cosx=1/2时,y(max)=2,x属于{x|x=(+,-)π/3+2kπ,k=0,(+,-)1,(+,-)2。}