Factor by grouping

G

Guest

Guest
What am I doing wrong?

2x^3 + x^2 - 8x -4

Here is what I have done:

2x^3 + x^2 -8x-4 grouping into two groups
2x(x + 1) -8x (x-2)
(2x + 1) (x-2)


My book says the answer is (2x + 1) (x-2) (x+2)
What would you say I did wrong?????? I appreciate your help. :)
 

dagr8est

Junior Member
Joined
Nov 2, 2004
Messages
128
2x^3+x^2-8x-4
=(2x^3-8x)+(x^2-4)
=2x(x^2-4)+1(x^2-4)
=(2x+1)(x^2-4)
=(2x+1)(x+2)(x-2)
 
G

Guest

Guest
2x^3 + x^2 -8x-4 grouping into two groups
2x(x + 1) -8x (x-2)
Expand that second line. Is it the same as the first line? No, that's where you went wrong.
 
G

Guest

Guest
Thank you

Thanks to both. Wish I me and my son where that smart! :)
 
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