Question 167669


Looking at the expression {{{6a^2-29a+9}}}, we can see that the first coefficient is {{{6}}}, the second coefficient is {{{-29}}}, and the last term is {{{9}}}.



Now multiply the first coefficient {{{6}}} by the last term {{{9}}} to get {{{(6)(9)=54}}}.



Now the question is: what two whole numbers multiply to {{{54}}} (the previous product) <font size=4><b>and</b></font> add to the second coefficient {{{-29}}}?



To find these two numbers, we need to list <font size=4><b>all</b></font> of the factors of {{{54}}} (the previous product).



Factors of {{{54}}}:

1,2,3,6,9,18,27,54

-1,-2,-3,-6,-9,-18,-27,-54



Note: list the negative of each factor. This will allow us to find all possible combinations.



These factors pair up and multiply to {{{54}}}.

1*54
2*27
3*18
6*9
(-1)*(-54)
(-2)*(-27)
(-3)*(-18)
(-6)*(-9)


Now let's add up each pair of factors to see if one pair adds to the middle coefficient {{{-29}}}:



<table border="1"><th>First Number</th><th>Second Number</th><th>Sum</th><tr><td  align="center"><font color=black>1</font></td><td  align="center"><font color=black>54</font></td><td  align="center"><font color=black>1+54=55</font></td></tr><tr><td  align="center"><font color=black>2</font></td><td  align="center"><font color=black>27</font></td><td  align="center"><font color=black>2+27=29</font></td></tr><tr><td  align="center"><font color=black>3</font></td><td  align="center"><font color=black>18</font></td><td  align="center"><font color=black>3+18=21</font></td></tr><tr><td  align="center"><font color=black>6</font></td><td  align="center"><font color=black>9</font></td><td  align="center"><font color=black>6+9=15</font></td></tr><tr><td  align="center"><font color=black>-1</font></td><td  align="center"><font color=black>-54</font></td><td  align="center"><font color=black>-1+(-54)=-55</font></td></tr><tr><td  align="center"><font color=red>-2</font></td><td  align="center"><font color=red>-27</font></td><td  align="center"><font color=red>-2+(-27)=-29</font></td></tr><tr><td  align="center"><font color=black>-3</font></td><td  align="center"><font color=black>-18</font></td><td  align="center"><font color=black>-3+(-18)=-21</font></td></tr><tr><td  align="center"><font color=black>-6</font></td><td  align="center"><font color=black>-9</font></td><td  align="center"><font color=black>-6+(-9)=-15</font></td></tr></table>



From the table, we can see that the two numbers {{{-2}}} and {{{-27}}} add to {{{-29}}} (the middle coefficient).



So the two numbers {{{-2}}} and {{{-27}}} both multiply to {{{54}}} <font size=4><b>and</b></font> add to {{{-29}}}



Now replace the middle term {{{-29a}}} with {{{-2a-27a}}}. Remember, {{{-2}}} and {{{-27}}} add to {{{-29}}}. So this shows us that {{{-2a-27a=-29a}}}.



{{{6a^2+highlight(-2a-27a)+9}}} Replace the second term {{{-29a}}} with {{{-2a-27a}}}.



{{{(6a^2-2a)+(-27a+9)}}} Group the terms into two pairs.



{{{2a(3a-1)+(-27a+9)}}} Factor out the GCF {{{2a}}} from the first group.



{{{2a(3a-1)-9(3a-1)}}} Factor out {{{9}}} 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.



{{{(2a-9)(3a-1)}}} Combine like terms. Or factor out the common term {{{3a-1}}}


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Answer:



So {{{6a^2-29a+9}}} factors to {{{(2a-9)(3a-1)}}}.



Note: you can check the answer by FOILing {{{(2a-9)(3a-1)}}} to get {{{6a^2-29a+9}}} or by graphing the original expression and the answer (the two graphs should be identical).