Question 658853: what are the stages to working out how to factorise 6x^2+13x+6. Do you have to work out the factors of 36 first?
Found 2 solutions by Shana-D77, MathLover1:
Answer by Shana-D77(132)   (Show Source):
You can put this solution on YOUR website! 6x^2+13x+6
My high school teachers told me to "guess and check" This method is a mess. Below is the method. Here's a video if the blow doesn't make sense: http://www.youtube.com/watch?v=tPkgssssMZQ
Ax^2 + Bx + c
6x^2+13x+6
A = 6
B = 13
C = 6
AC = 36
Q: What numbers add to get B that multiply to get AC?
A: 4*9
Now rewrite with 9 and 4:
6x^2+13x+6
6x^2 + 4x + 9x + 6
Now parenthesize:
(6x^2 + 4x) + (9x + 6)
Mpw factor each ( ), leavig thet + in the middle:
2x(3x + 2) + 3(3x + 2)
The ( ) will always be the same. When in doubt, let your first ( ) lead the way to finding your second one.
Now, write the stuff on the outside of the ( ): "2x + 3":
(2x + 3)
Next to one of the inside ( ):
(3x + 2)
So you have:
(2x + 3)(3x + 2)
Answer by MathLover1(20850)  (Show Source):
You can put this solution on YOUR website!
| Solved by pluggable solver: Factoring using the AC method (Factor by Grouping) |
Looking at the expression  , we can see that the first coefficient is  , the second coefficient is  , and the last term is .
Now multiply the first coefficient by the last term to get  .
Now the question is: what two whole numbers multiply to  (the previous product) and add to the second coefficient ?
To find these two numbers, we need to list all of the factors of (the previous product).
Factors of :
1,2,3,4,6,9,12,18,36
-1,-2,-3,-4,-6,-9,-12,-18,-36
Note: list the negative of each factor. This will allow us to find all possible combinations.
These factors pair up and multiply to .
1*36 = 36
2*18 = 36
3*12 = 36
4*9 = 36
6*6 = 36
(-1)*(-36) = 36
(-2)*(-18) = 36
(-3)*(-12) = 36
(-4)*(-9) = 36
(-6)*(-6) = 36
Now let's add up each pair of factors to see if one pair adds to the middle coefficient :
| First Number | Second Number | Sum | | 1 | 36 | 1+36=37 | | 2 | 18 | 2+18=20 | | 3 | 12 | 3+12=15 | | 4 | 9 | 4+9=13 | | 6 | 6 | 6+6=12 | | -1 | -36 | -1+(-36)=-37 | | -2 | -18 | -2+(-18)=-20 | | -3 | -12 | -3+(-12)=-15 | | -4 | -9 | -4+(-9)=-13 | | -6 | -6 | -6+(-6)=-12 |
From the table, we can see that the two numbers  and  add to (the middle coefficient).
So the two numbers and both multiply to and add to
Now replace the middle term  with  . Remember, and add to . So this shows us that  .
 Replace the second term with .
 Group the terms into two pairs.
 Factor out the GCF  from the first group.
 Factor out  from the second group. The goal of this step is to make the terms in the second parenthesis equal to the terms in the first parenthesis.
 Combine like terms. Or factor out the common term 
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Answer:
So  factors to .
In other words,  .
Note: you can check the answer by expanding to get or by graphing the original expression and the answer (the two graphs should be identical).
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