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Solve f(x) = 2x^2 -x -15 by factoring.

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nadooosh | Student, Undergraduate | eNoter

Posted January 9, 2011 at 10:00 AM via web

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Solve f(x) = 2x^2 -x -15 by factoring.

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hala718 | High School Teacher | (Level 1) Educator Emeritus

Posted January 9, 2011 at 10:04 AM (Answer #1)

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Given the function f(x) = 2x^2 -x -15

We need to solve for x by factoring.

First we have a quadratic equation. Then we can simplify into two factor.

==> f(x) = 2x^2 -x -15

We will try and determine one of the roots.

We will substitute with x=3.

==> f(3) = 2*9 0-3 -15 = 0

==> X=3 is one of the roots.

Then (x-3) is one of the factor.

==> f(x) = (x-3) * R(x)

Now, to find the other factor, we will divide f(x) by (x-3).

==> f(x) = (x-3)(2x+5)

==> x1= 3

==> x2= -5/2

 

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted January 9, 2011 at 10:28 AM (Answer #2)

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We have to solve f(x) = 2x^2 -x -15 by factoring.

Now we see that -1 can be written as 5 - 6 = -1. Here 5*-6 = -30.

f(x) = 2x^2 -x -15 = 0

=> 2x^2 - 6x + 5x - 15 = 0

=> 2x(x - 3) + 5(x - 3) = 0

=> (2x + 5)(x - 3) = 0

For 2x + 5 = 0

=> x = -5/2

And for x - 3 = 0

=> x= 3

Therefore x is equal to -5/ 2 and 3.

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maria-vivanco | TA , Grade 11 | Valedictorian

Posted July 30, 2014 at 10:24 PM (Answer #3)

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-5/ 2 and 3.

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