Thursday, October 23, 2014

Please explain why x> 3 or x3 or x> 2?Consider the question: Solve for x in lR, X^2 -5x + 6 >0

For the inequality:


x^2 - 5x
+6 > 0


First we will
factor:


==> (x-2)(x-3) >
0


Now we have a product of two function. In order for the
product of two numbers to be positive ( > 0) then both numbers should be positive
or both numbers should be negative.


Then we have two
options:


(x-2) > 0  AND   x-3 >
0


We will solve.


==> x
> 2   AND  x > 3


==> x = (2, inf) n (
3, inf) = (3,in)


==> x = (3, inf )
............(1)


For the second
option:


(x-2) < 0  AND   (x-3) <
0


==> x < 2  AND   x <
3


==> x = (-inf , 2) n (-inf, 3) = (-inf,
2)


==> x = (-inf, 2)
.............(2)


Then, we have two possible
solutions
: (1) and (2).


==> x = (-inf
, 2) U ( 3, inf)


OR:   x <2  OR  x
> 3

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