Thursday, December 3, 2015

Solve the quadratic inequality 3x^2-13x-10>0.

To solve the inequality above, first we have to calculate
the roots of the equation 3x^2-13x-10 = 0.


After finding
the roots of the equation, we could write the expression in a factored form
as:


3(x-x1)(x-x2)>0


So,
let's apply the quadratic formula to calculate the
roots:


x1 =
[13+sqrt(169-120)]/6


x1 =
(13+sqrt49)/6


x1 =
(13+7)/6


x1 =
10/3


x2 =
(13-7)/6


x2 =
6/6


x2 =
1


The inequality will be written
as:


3(x -
10/3)(x-1)>0


We'll divide by
3:


(x -
10/3)(x-1)>0


Now, we'll discuss the
inequality:


- the product is positive if the factors are
both positive:


x -
10/3>0


x>10/3


and


x-1>0


x>1


So,
x belongs to the interval (10/3 , +inf.)


- the product is
positive if the factors are both negative:


x -
10/3<0


x<10/3


x-1<0


x<1


So,
x belongs to the interval ( -inf.,1)


Finally, the solution
set of the inequality is the union of the sets identified
above:


( -inf.,1) U (10/3 ,
+inf.)

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