maths表達問題
回答 (3)
2013-03-05 7:27 am
✔ 最佳答案
a > 2a - 2 > 0 ..... (1)
b < - 2
b + 2 < 0 .....(2)
(1) and (2) :
b + 2 < 0 < a - 2
b + 2 < a - 2
a - b > 4 ..... (3)
(1)*(2) :
(a - 2) (b + 2) < 0
ab + 2a - 2b - 4 < 0
2(a - b) < 4 - ab ..... (4)
(3) and (4) :
8 < 2(a - b) < 4 - ab
8 < 4 - ab
ab < - 4
2013-03-05 00:18:56 補充：
Alternatively :
a > 2 , b < - 2 or - b > 2
So
a (-b) > 2 * 2
ab < - 4
2013-03-07 11:36 pm
a > 2
a - 2 > 0 ..... (1)
b < - 2
b + 2 < 0 .....(2)
(1) and (2) :
b + 2 < 0 < a - 2
b + 2 < a - 2
a - b > 4 ..... (3)
(1)*(2) :
(a - 2) (b + 2) < 0
ab + 2a - 2b - 4 < 0
2(a - b) < 4 - ab ..... (4)
(3) and (4) :
8 < 2(a - b) < 4 - ab
8 < 4 - ab
ab < - 4
a - 2 > 0 ..... (1)
b < - 2
b + 2 < 0 .....(2)
(1) and (2) :
b + 2 < 0 < a - 2
b + 2 < a - 2
a - b > 4 ..... (3)
(1)*(2) :
(a - 2) (b + 2) < 0
ab + 2a - 2b - 4 < 0
2(a - b) < 4 - ab ..... (4)
(3) and (4) :
8 < 2(a - b) < 4 - ab
8 < 4 - ab
ab < - 4
2013-03-07 2:21 am
a > 2
a - 2 > 0 ..... (1)
b < - 2
b + 2 < 0 .....(2)
(1) and (2) :
b + 2 < 0 < a - 2
b + 2 < a - 2
a - b > 4 ..... (3)
(1)*(2) :
(a - 2) (b + 2) < 0
ab + 2a - 2b - 4 < 0
2(a - b) < 4 - ab ..... (4)
(3) and (4) :
8 < 2(a - b) < 4 - ab
8 < 4 - ab
ab < - 4
2013-03-06 18:22:09 補充：
Alternatively :
a > 2 , b < - 2 or - b > 2
So
a (-b) > 2 * 2
ab < - 4
a - 2 > 0 ..... (1)
b < - 2
b + 2 < 0 .....(2)
(1) and (2) :
b + 2 < 0 < a - 2
b + 2 < a - 2
a - b > 4 ..... (3)
(1)*(2) :
(a - 2) (b + 2) < 0
ab + 2a - 2b - 4 < 0
2(a - b) < 4 - ab ..... (4)
(3) and (4) :
8 < 2(a - b) < 4 - ab
8 < 4 - ab
ab < - 4
2013-03-06 18:22:09 補充：
Alternatively :
a > 2 , b < - 2 or - b > 2
So
a (-b) > 2 * 2
ab < - 4
參考: me
收錄日期: 2021-04-21 22:27:35
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