已知,x^2-xy-2y^2=x-2y,且x-2y不等于0,则(1)x+y=(2若题中)x、y满足等式x^2+y^2-9x+5y+26=0,请确定x、y的值

Question

已知,x^2 -xy-2y^2 =x-2y,且x-2y不等于0,则(1)x+y=________(2若题中)x、y满足等式x^2 +y^2 -9x+5y+26=0,请确定x、y的值

Answer 1

x²-xy-2y²=x-2y
x²-xy-2y²-(x-2y)=0
(x-2y)(x+y)-(x-2y)=0
(x-2y)(x+y-1)=0
x-2y≠0,因此只有x+y-1=0
x+y=1
y=1-x
x²+y²-9x+5y+26=0
y=1-x代入,整理,得
x²-8x+16=0
(x-4)²=0
x=4
y=1-x=1-4=-3
x=4 y=-3