คำตอบ

2014-02-20T18:59:04+07:00
2x²-5xy+2y²=5 2x-y=1...      2x²-5xy+2y²=5  2x-y=1                                                                                                  
2014-02-20T20:38:30+07:00
2x²-5xy+2y²=5__(1)
2x-y=1__(2)
จากสมการ(2);y=2x-1__(3)
แทน(3)ใน(1);2x²-5x(2x-1)+2(2x-1)²=5
2x²-10x²+5x+2(4x²-4x+1²)=5
-3x=3x
x=-1
แทนx=-1ใน(2);2(-1)-y=1
                             y=-3
ดังนั้น(x,y)=(-1,-3)