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May 29, 2015

May 29, 2015

Posted by **Giselle** on Monday, February 14, 2011 at 10:32pm.

x^3-5x^2-14x<0

- Pre Calc -
**Reiny**, Monday, February 14, 2011 at 11:53pmx^3-5x^2-14x<0

x(x^2 - 5x - 14) < 0

x(x-7)(x+2) < 0

so we have 3 critical values:

x = 0, -2, and 7

investigate each domain

1. x < -2 , I will pick x = -5

(-)(-)(-) which is < 0 , that works

2. between -2 and 0, I will pick x = -1

(-)(-1)(+) > 0 , no good

3. between 0 and 7, I will pick x = 1

(+)(-)(+) < 0 , yup, that works

4. x > 7, I will pick x = 10

(+)(+)(+) > 0 , no good

so x < -2 OR 0 < x < 7

notice I did not actually have to find the algebraic answer, just determine if the result is + or -

- Pre Calc -
**Giselle**, Tuesday, February 15, 2011 at 7:50amthanks!