Monday, September 12, 2011

For what values of x is the following inequation valid : 2x^2 + x - 3

We are given the following inequation to solve 2x^2 + x -
3 < 0


2x^2 + x - 3 <
0


=> 2x^2 + 3x -2x -3 <
0


=> x ( 2x +3) -1 (2x + 3)
<0


=> (x - 1)(2x + 3)
<0


Now as ( x - 1)(2x + 3) is less than 0, either
 (x - 1) < 0 and (2x + 3) >0 or (x - 1) > 0 and (2x + 3) <
0.


For the first case:


(x - 1)
< 0 and (2x + 3) >0


=> x < 1
and x > -3/2


Therefore x takes values less than 1
and greater than -3/2 , or x lies in (-3/2 , 1)


For the
second case:


(x - 1) > 0 and (2x + 3) <
0


=> x > 1 and x <
-3/2


This implies x has to be simultaneously greater than 1
and less than -3/2, which is not possible.


So we cannot
obtain any values for x here.


Therefore the
possible values for x are ( -3/2 , 1)

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