若(x+y-5)^2+lx-y+3l=0,则 x^2-y^2=?,现在回答,

问题描述:

若(x+y-5)^2+lx-y+3l=0,则 x^2-y^2=?,现在回答,

(x+y-5)^2+lx-y+3l=0,
x+y-5=0 x-y+3=0
x+y=5 x-y=-3
x^2-y^2=(x+y)(x-y)=5*(-3)=-15可以帮我在算一题吗若x+y=-5,xy=6,则x的平方+y的平方=?