50. 令  ，試求 xyz + 3＝？
(A)2
(B)5
(C)6
(D)3

答案：登入後查看
統計： A(324), B(110), C(110), D(92), E(0) #670273

詳解 (共 4 筆)

#1407257
php8V88MS
48
0
#3439912

偷吃步

令X=1/2，則Y要=2

若Y=2則Z=-1

所以XYZ+3=-1+3=2

12
0
#1396322
參考：https://www.ptt.cc/bbs/Math/M.1376452877.A.950.html
x+1/y=1--> xy=y-1 (1)
y+1/z=1--> yz+1=z (2)
xyz=xy * z
= (y-1)*z (參照(1))  
= yz-z (參照(2)  
 = -1  
所以xyz+3=2
5
0
#3413954

( x + 1/y )( y + 1/z )=1

→xy + 1 + x/z + 1/yz = 1

→ xyz + x + 1/y =0

→ xyz + 1 = 0

→ xyz = -1

xyz + 3 = -1 + 3 = 2

5
0