若x-y=1,xy=5,则x²y-xy²=?已知a+b=3,a²b+ab²=1,则ab=?

若x-y=1,xy=5,则x²y-xy²=?
已知a+b=3,a²b+ab²=1,则ab=?

解
x²y-xy²
=xy(x-y)
=5×1
=5
a²b+ab²=1
∴ab(a+b)=1
∵a+b=3
∴3ab=1
∴ab=1/3