已知x+y=3 xy=2求代数式-x2y-xy2的值 (2)已知x+5y=6求x²+5xy+30y的值

题目

已知x+y=3 xy=2求代数式-x2y-xy2的值 (2)已知x+5y=6求x²+5xy+30y的值

答案

1）-x^2y-xy^2
=-xy(x+y)
=-2×3
=-6
2）x²+5xy+30y
=x(x+5y)+30y
=6x+30y
=6(x+5y)
=6×6
=36