Question 336163


Looking at the expression {{{4x^2+24x+9}}}, we can see that the first coefficient is {{{4}}}, the second coefficient is {{{24}}}, and the last term is {{{9}}}.



Now multiply the first coefficient {{{4}}} by the last term {{{9}}} to get {{{(4)(9)=36}}}.



Now the question is: what two whole numbers multiply to {{{36}}} (the previous product) <font size=4><b>and</b></font> add to the second coefficient {{{24}}}?



To find these two numbers, we need to list <font size=4><b>all</b></font> of the factors of {{{36}}} (the previous product).



Factors of {{{36}}}:

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 {{{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


Now let's add up each pair of factors to see if one pair adds to the middle coefficient {{{24}}}:



<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>36</font></td><td  align="center"><font color=black>1+36=37</font></td></tr><tr><td  align="center"><font color=black>2</font></td><td  align="center"><font color=black>18</font></td><td  align="center"><font color=black>2+18=20</font></td></tr><tr><td  align="center"><font color=black>3</font></td><td  align="center"><font color=black>12</font></td><td  align="center"><font color=black>3+12=15</font></td></tr><tr><td  align="center"><font color=black>4</font></td><td  align="center"><font color=black>9</font></td><td  align="center"><font color=black>4+9=13</font></td></tr><tr><td  align="center"><font color=black>6</font></td><td  align="center"><font color=black>6</font></td><td  align="center"><font color=black>6+6=12</font></td></tr><tr><td  align="center"><font color=black>-1</font></td><td  align="center"><font color=black>-36</font></td><td  align="center"><font color=black>-1+(-36)=-37</font></td></tr><tr><td  align="center"><font color=black>-2</font></td><td  align="center"><font color=black>-18</font></td><td  align="center"><font color=black>-2+(-18)=-20</font></td></tr><tr><td  align="center"><font color=black>-3</font></td><td  align="center"><font color=black>-12</font></td><td  align="center"><font color=black>-3+(-12)=-15</font></td></tr><tr><td  align="center"><font color=black>-4</font></td><td  align="center"><font color=black>-9</font></td><td  align="center"><font color=black>-4+(-9)=-13</font></td></tr><tr><td  align="center"><font color=black>-6</font></td><td  align="center"><font color=black>-6</font></td><td  align="center"><font color=black>-6+(-6)=-12</font></td></tr></table>



From the table, we can see that there are no pairs of numbers which add to {{{24}}}. So {{{4x^2+24x+9}}} cannot be factored.



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<a name="ans">


Answer:



So {{{4x^2+24x+9}}} doesn't factor at all (over the rational numbers).



So {{{4x^2+24x+9}}} is prime.



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Jim