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How do I factor 4x^3 - 15x^2 + 2x +21

Guest Jun 12, 2014

Best Answer 

 #3
avatar+86859 
+5

I actually used WolframAlpha....we could try some synthetic division - plugging in all the possible factors of 21 over all the possible factors of 4 ... this could be a little time consuming. However, I see that 1 is not a root, so I might test -1...so we have....

-1     4   -15        2        21

               -4       19     -21

        4     -19      21        0

 

So....-1 is a root....and we have the 2nd degree polynomial ......4x^2 -19x +21

Factoring this, we have   (4x -7) (x-3)

So, the factorization is   (x+1)(4x-7)(x-3)

Sorry for not being more thorough the first time, but I was in a hurry  !!!

CPhill  Jun 13, 2014
 #1
avatar+86859 
+5

4x^3 - 15x^2 + 2x +21 =

(4x-7)(x+1)(x-3)

 

CPhill  Jun 13, 2014
 #2
avatar+92623 
0

Hey Chris,

Are you going to show this person how you got your answer?

Melody  Jun 13, 2014
 #3
avatar+86859 
+5
Best Answer

I actually used WolframAlpha....we could try some synthetic division - plugging in all the possible factors of 21 over all the possible factors of 4 ... this could be a little time consuming. However, I see that 1 is not a root, so I might test -1...so we have....

-1     4   -15        2        21

               -4       19     -21

        4     -19      21        0

 

So....-1 is a root....and we have the 2nd degree polynomial ......4x^2 -19x +21

Factoring this, we have   (4x -7) (x-3)

So, the factorization is   (x+1)(4x-7)(x-3)

Sorry for not being more thorough the first time, but I was in a hurry  !!!

CPhill  Jun 13, 2014

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