y=Sin3x-Sin(π/2-3x)=2Cos[(3x+π/2-3x)/2]Sin[(3x+π/2+3x)/2]=2Cos(π/4)Sin(3x+π/4)=√2Sin(3x+π/4)所以最大值是√2当且仅当3x+π/4=2kπ+(π/2)时取到,(k=1,2,3,……)此时x=(2/3)kπ+(π/12),(k=1,2,3,……)...