解题:已知x+Y=5,xy=3,求x^5+Y^5
x^2+y^2=(x+y)^2-2xy=19
x^3+y^3=(x+y)(x^2-xy+y^2)
=5*(19-3)=80
x^5+y^5
=(x^2+y^2)*(x^3+y^3)-x^2*y^2*(x+y)
=19*80-9*5
=1520-45
=1475
x^2+y^2=(x+y)^2-2xy=19
x^3+y^3=(x+y)(x^2-xy+y^2)
=5*(19-3)=80
x^5+y^5
=(x^2+y^2)*(x^3+y^3)-x^2*y^2*(x+y)
=19*80-9*5
=1520-45
=1475