不等式數學問題

There are 2 mistakes:
(1)You tried to multiply both side by x, but x is not equal to -2, it can be any value greater than -2, so you should not multiply the right hand side by -2.
(2) Since x is greater than -2, it can be positive or negative, so if you multiply the inequality by x, you may have changed the sign of the inequality.

2008-07-05 21:54:22 補充：
Condition 2 of 002 has a problem. Let x = 1 which is greater than 0, but 1^2 = 1 is not greater than 4!

2008-07-06 10:48:48 補充：
x^2 is greater than 4 only if x is greater than 2 or less than -2. So if you want x^2 to be greater than 4 and at the same time x is greater than -2, so x must be greater than +2. Note that x^2 cannot be greater than 4 in the range -2 to +2.

x^2＞(- 2)^2 <<呢步炒左 becoz冇考慮x係負數

so要咁做...

情況1: -2< x < 0

x^2 < (-2)^2 ( rule: a>b , ac < bc when c<0)

x^2 < 4

情況2 : x>= 0

x^2＞(- 2)^2

x^2 > 4