2x(5-3x)=10X-6X^2=-6X^2+10X
=-6(X^2-5/3X)=-6(X^2-5/3X+25/36-25/36)
=-6[(X-5/6)^2-25/36]
=-6(X-5/6)^2+25/6
因为0小于X小于3分之5,故当X=5/6时,有最大值25/6
当X=0或5/3时,有最小值0