{x^2+y^2=12 x+y=5

题目

{x^2+y^2=12 x+y=5
{x^2-y^2+x-y-6=0 x^2-y^2-x+y-4=0
{x^2/4-y^2=1 x-y-2=0
{(x-3)^2+y^2=9 x+2y=0
{x^2+y^2-4x-3y+5=0 3x^2+3y^2-11x-7y+10=0
{(x+y)(x-2y)=-5 (x-y)(x+2y)=7
{x+y+xy=7 x^2+y^2+xy=13
{x^2+y^2=10 x+xy+y=7

答案

一、x^2+y^2=12① x+y=5②
②式变为x=5-y代入①式,得,2y^2-10y+25=12解得y无解（△=b^2-4ac