Question

Answer 1

1: x+2y=7

=>x=7-2y=-2y+7

\(x^2+2y^2-2xy=5\)

=>\(\left(-2y+7\right)^2+2y^2-2y\left(-2y+7\right)=5\)

=>\(4y^2-28y+49+2y^2+4y^2-14y-5=0\)

=>\(10y^2-42y+44=0\)

=>\(5y^2-21y+22=0\)

=>\(5y^2-10y-11y+22=0\)

=>(y-2)(5y-11)=0

=>y=2 hoặc y=2,2

TH1: y=2

x=-2y+7=-2*2+7=3

TH2: y=2,2

x=-2y+7=-2*2,2+7=-4,4+7=2,6

2: 2x-y-7=0

=>y=2x-7

\(y^2-x^2+2x+2y+4=0\)

=>\(\left(2x-7\right)^2-x^2+2x+2\left(2x-7\right)+4=0\)

=>\(4x^2-28x+49-x^2+2x+4x-14+4=0\)

=>\(3x^2-22x+39=0\)

=>\(3x^2-13x-9x+39=0\)

=>(3x-13)(x-3)=0

=>x=3 hoặc x=13/3

TH1: x=3

=>y=2x-7=2*3-7=-1

TH2: x=13/3

=>y=2x-7=2*13/3-7=26/3-7=5/3