Posted by **Amy~** on Wednesday, September 29, 2010 at 9:42pm.

I don't get when you use "or" or "and" in inequalities.

Like for this quadratic inequality:

x^(2) +x -12 > 0

becomes x < -4

x > 3

why is the answer {x|x<-4 or x>3} and not {x|3<x<-4} ?

- Math -
**Henry**, Wednesday, September 29, 2010 at 10:40pm
Your quadratic inequality has TWO solutions: x < -4 AND x > 3.

The 2nd arrangement where you have x in the center of the inequality is normally used with compound inequalities.

- Math -
**MathMate**, Thursday, September 30, 2010 at 12:54am
If you look at the graph, it would be clear that the part of the curve which is above the x-axis is in two separate parts, therefore the answer is

x<-4 and x>3.

On the other hand if the question had been x^(2) +x -12 < 0 , then the solution will be continuous on the number line, namely -4<x<3.

See graph:

http://img529.imageshack.us/img529/2064/1285810976.png

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