In order to factor  , first we need to ask ourselves: What two numbers multiply to 36 and add to 13? Lets find out by listing all of the possible factors of 36
Factors:
1,2,3,4,6,9,12,18,36,
-1,-2,-3,-4,-6,-9,-12,-18,-36,List the negative factors as well. This will allow us to find all possible combinations
These factors pair up to multiply to 36.
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
note: remember two negative numbers multiplied together make a positive number
Now which of these pairs add to 13? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to 13
| 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 | We can see from the table that 4 and 9 add to 13. So the two numbers that multiply to 36 and add to 13 are: 4 and 9
Now we substitute these numbers into a and b of the general equation of a product of linear factors which is:
 substitute a=4 and b=9
So the equation becomes:
(x+4)(x+9)
Notice that if we foil (x+4)(x+9) we get the quadratic again
Just replace the x's with a's to get:
Set each term to zero
So our answer is
or
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