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this is how i did this one

i did   4x^2 times 8  so i get    32  

now i have    -12x + 32 

2 factors of 32 that give -12 are -4 and - 8 

so the final answer would be    (x-4)(x-8)   but it wouldn't give me 4x^2 - 12x + 8  

 Sep 6, 2014

Best Answer 

 #2
avatar+118677 
+5

Anonymous, your exact method will only work if the coefficient of x2 is 1.

When factorising always look for common factors first like Honga has done.

If there are no common factors - I mean when I cannot get the x2 coefficient to equal 1 I use the  grouping method technique.

This video is good for factoring all types of quadratics.

https://www.youtube.com/watch?v=ZQ-NRsWhOGI

 Sep 6, 2014
 #1
avatar+169 
+5

By taking out a common factor they mean getting rid of a common factor, 4, 12 and 8 can all be divided by 4:

 

$$4x^2-12x+8=4(x^2-3x+2)$$

 

$$4(x^2-3x+2)=4(x-2)(x-1)$$

 

Hope this helps.

 Sep 6, 2014
 #2
avatar+118677 
+5
Best Answer

Anonymous, your exact method will only work if the coefficient of x2 is 1.

When factorising always look for common factors first like Honga has done.

If there are no common factors - I mean when I cannot get the x2 coefficient to equal 1 I use the  grouping method technique.

This video is good for factoring all types of quadratics.

https://www.youtube.com/watch?v=ZQ-NRsWhOGI

Melody Sep 6, 2014

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