Question

已知x+y-2=0,2yy-y-4=0,求y-x/y的值?

速度回

Answer 1

解：∵x+y-2=0,x+y=2
∴2y²-y-4=0,2y²-y-2x-2y=0，2y²-2x-3y=0
∵2y²-y-4=0
∴y≠0
2y²-2x-3y=0两边同时除以y
2y-2x/y=3
y-x/y=1.5

Answer 2

y-x/y变形得：(y^2-x)/y
由题意x+y-2=0得x=2-y
2y^2-y-4=0得y^2=2+y/2
将这两个代入变形后的式子得：(y^2-x)/y
={2+y/2-(2-y)}/y
={2+y/2-2+y}/y
=3y/2y
=3/2
=1.5