方程组{x^2+xy-2y^2=0{x^2+4y=-2 解的个数是( )a.1 b.2 c.3 d.4

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方程组{x^2+xy-2y^2=0{x^2+4y=-2解的个数是()a.1b.2c.3d.4方程组{x^2+xy-2y^2=0{x^2+4y=-2解的个数是()a.1b.2c.3d.4方程组{x^2+

方程组{x^2+xy-2y^2=0{x^2+4y=-2 解的个数是( )a.1 b.2 c.3 d.4
方程组{x^2+xy-2y^2=0
{x^2+4y=-2 解的个数是( )
a.1 b.2 c.3 d.4

方程组{x^2+xy-2y^2=0{x^2+4y=-2 解的个数是( )a.1 b.2 c.3 d.4
x^2+xy-2y^2=0
x^2+xy + 1/4 y^2 = 9/4 y^2
(x+y/2)^2 = (3y/2)^2
x+y/2 = ±3y/2
=>x=y或-2y
1.当x=y时
x^2+4y=-2
=>
y^2+4y+2=0
△=16-8=8>0,有两个根
2.当x=-2y时
x^2+4y=-2
=>
4y^2+4y+2=0
△=16-32=-16

把数带进去,哪个成立就对