因为x+y=5,所以(x+y)^2=x^2+y^2+2xy=25(1)
将x^2+y^2=13代入(1)式求得xy=6
x^3y+2x^2y^2+xy^3=xy(x^2+2xy+y^2)
=6(x+y)^2
=6*25
=150