2x-y+1=0;
y²+4y+4=0；
（y+2）²=0;
y=-2;
2x=y-1;
2x=-3;
x=-3/2;
1-x-2y分之x-y÷x的平方-4xy+4y
=1-(x-y)/(x-2y)-y/(x-2y)²
=(-y)/(x-2y)-y/(x-2y)²
=(-xy+2y²-y)/(x-2y)²
=((3/2)×(-2)+8+2)/(-3/2+4)²
=28/25;
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