已知x^4+y^4=50,x^2y-xy^2=14,求代数式x^4-y^4+3xy^2-5x^2y+3x^2y+2y^4的值
问题描述：
已知x^4+y^4=50,x^2y-xy^2=14,求代数式x^4-y^4+3xy^2-5x^2y+3x^2y+2y^4的值
答
x^4- y^4+3xy^2-xy^2-5x^2y+3x^2y+2y^4
=x^4+ y^4+2xy^2-2x^2y
=50-2*(-14)
=78