Wednesday, November 6, 2013

inequality

Solve the inequality:


(|x|-2)2 >= x+4


(|x|-2)2 >= x+4
Or, (|x|2-4|x|+4) >= x+4
Or, (x2-4|x|+4) >= x+4 ………………because |x|2= x2
Substituting |x| = +x and |x|= -x and solving the above inequality
For, |x| = +x
x2-4x+4 >= x+4
Or, x2-5x>= 0
Or, x(x – 5)>=0,
so, x >= 0 or, x >= 5,  OR x <= 0 or, x <= 5
so, general solution x >= 5, or x <= 0        --------------------(1)
For, |x| = -x
x2+4x+4 >= x+4
Or, x2+3x>= 0
Or, x(x +3)>=0,
so, x >= 0 or, x >= -3, OR x <= 0 or, x <= -3
so, general solution x >= 0, or x <= -3  -------------------(2)
on combining (1) and (2), we have
x <= -3  or x >= 5
 

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