Y=（cosX)^2 + sinXcosX= (2(cosX)^2-1)/2 + 1/2 + (1/2)sin2X= (1/2)cos2X + (1/2)sin2X + 1/2= (1/2)sin(2X + pi/4 ) + 1/2(1/2)sin(2X + pi/4 )值域为 -1/2 到 1/2的闭区间那y就是值域为 0 到 1 的闭区间....