x+y=4 , xy= -2 ,then(x^ -1+y^ -1)= ??
A. -2
B 2
C -1/2
D 1/2
E 1
F.3 maths question
2007-10-21 8:10 pm
回答 (3)
2007-10-21 8:18 pm
✔ 最佳答案
(x^ -1+y^ -1)=x分之一加y分之一
加減要通分母
x+y
------（分數）
xy
4
---=2
2
2007-10-21 12:20:12 補充：
答案是B.2
2007-10-22 20:20:10 補充：
睇漏左個負號，應該是4---=-2-2 A.2才是
2007-10-22 12:58 am
1/x+1/y
=y/xy+x/xy
=y+x/xy
Since, x+y=4,xy=-2,sub. in the equation:
=4/-2
= - 4/2
= - 2//
The answer of this equation is -2.
The answer -2 satisfies the equation.
The m.c answer is A (-2).
=y/xy+x/xy
=y+x/xy
Since, x+y=4,xy=-2,sub. in the equation:
=4/-2
= - 4/2
= - 2//
The answer of this equation is -2.
The answer -2 satisfies the equation.
The m.c answer is A (-2).
參考: me.
2007-10-21 9:10 pm
(x^ -1+y^ -1)
= 1/x + 1/y
= (x+y)/(xy)
=4/(-2) (given, x+y=4 , xy= -2 )
=-2
ANS: A
= 1/x + 1/y
= (x+y)/(xy)
=4/(-2) (given, x+y=4 , xy= -2 )
=-2
ANS: A
收錄日期: 2021-04-13 14:04:52
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