Question

若x-y=2,2y^2+y-4=0,求x/y-y的值

过程一定要清楚

Answer 1

解：由2y^2+y-4=0,得，y^2=2-y/2①
由x-y=2.得，x-2=y②
x/y-y
=x/y-y^2/y
=(x-y^2)/y
=[x-(2-y/2)]/y(将①代人)
=(x-2+y/2)/y
=(y+y/2)/y（将②代人）
=(3y/2)/y
=3/2

Answer 2

解：x/y-y
=X/Y-Y^2/Y
=（X-Y^2）/Y
=(2X-2Y^2)/2Y （分子分母同时X2）
=[2(Y+2)-(4-Y)]/2Y (把X=Y+2, 2Y^2=4-Y代入)
=(2Y-4-4+Y)/2Y
=3Y/2Y
3/2