Question

数学分式

先化简2a-（a+1)+a-1分之a的平方-1，再选择你喜欢的且又合适的数代入求值。

若x分之1-y分之一=3，求x-2xy-y分之2x-3xy-2y的值

Answer 1

2a - (a+1) + (a^2-1)/(a-1)
=2a - (a+1) + (a+1)(a-1)/(a-1)
=2a -a-1 + a+1
=2a
令a=8
2a=2*8=16

1/x - 1/y = 3

(2x-3xy-2y)/(x-2xy-y)
分子分母同除以xy：
=(2/y-3-2/x)/(1/y-2-1/x)
={-3-2(1/x-1/y)} / {-2-(1/x-1/y)}
={-3-2*3} / {-2-3}
=(-9) / (-5)
=9/5