Q34:

The operation Θ is defined by x Θ y = 1/x + 1/y for all nonzero numbers x and y.  If z is a number greater than 1, which of the following must be true?

I.  x Θ (-z) = 0

I.  x Θ (-z) = 0

II.  z Θ z/(z-1)= 1

III.  2/z Θ 2/z = z

A.    I only

B.    I and II only

C.    I and III only

D.    II and III only

E.    I, II, and III

答案是e, 請8有沒有人可解答?especial for 1 and 3.

之前有人問過,但打錯題目, 謝謝