[問題]GWD gmat 8

[blacklilu]

Q8:
The operation @ is defined for all nonzero numbers a and b by a @b = a/b – b/a. If x and y are nonzero numbers, which of the following statements must be true?


I. x @xy = x(1 @ y)
II. x @y = -(y@x)
III. 1/x @1/y = y @ x


A. I only
B. II only
C. III only
D. I and II
E. II and III

does someone tell me how to do this one ?
tks

[marco]

這個是通式a @b = a/b – b/a...所以將xy帶入
I. x @xy = x(1 @ y)
先算右邊括號裡的東西...a帶1,b帶y,則為(1/y-y)
x@xy=x(1/y-y)
x@xy=x/y-xy
再算左邊
a帶x,b帶xy.....則為(1/y-y)
故1/y-y不等於x(1/y-y)....因為x不確定
II. x @y = -(y@x)
III. 1/x @1/y = y @ x
II.III如法炮製....可得II,III是符合的
如果不懂再發問吧~~