Question 207857

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{{{8t^4+75t^3+27t^2}}} Start with the given expression.



{{{t^2(8t^2+75t+27)}}} Factor out the GCF {{{t^2}}}.



Now let's try to factor the inner expression {{{8t^2+75t+27}}}



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Looking at the expression {{{8t^2+75t+27}}}, we can see that the first coefficient is {{{8}}}, the second coefficient is {{{75}}}, and the last term is {{{27}}}.



Now multiply the first coefficient {{{8}}} by the last term {{{27}}} to get {{{(8)(27)=216}}}.



Now the question is: what two whole numbers multiply to {{{216}}} (the previous product) <font size=4><b>and</b></font> add to the second coefficient {{{75}}}?



To find these two numbers, we need to list <font size=4><b>all</b></font> of the factors of {{{216}}} (the previous product).



Factors of {{{216}}}:

1,2,3,4,6,8,9,12,18,24,27,36,54,72,108,216

-1,-2,-3,-4,-6,-8,-9,-12,-18,-24,-27,-36,-54,-72,-108,-216



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



These factors pair up and multiply to {{{216}}}.

1*216 = 216
2*108 = 216
3*72 = 216
4*54 = 216
6*36 = 216
8*27 = 216
9*24 = 216
12*18 = 216
(-1)*(-216) = 216
(-2)*(-108) = 216
(-3)*(-72) = 216
(-4)*(-54) = 216
(-6)*(-36) = 216
(-8)*(-27) = 216
(-9)*(-24) = 216
(-12)*(-18) = 216


Now let's add up each pair of factors to see if one pair adds to the middle coefficient {{{75}}}:



<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>216</font></td><td  align="center"><font color=black>1+216=217</font></td></tr><tr><td  align="center"><font color=black>2</font></td><td  align="center"><font color=black>108</font></td><td  align="center"><font color=black>2+108=110</font></td></tr><tr><td  align="center"><font color=red>3</font></td><td  align="center"><font color=red>72</font></td><td  align="center"><font color=red>3+72=75</font></td></tr><tr><td  align="center"><font color=black>4</font></td><td  align="center"><font color=black>54</font></td><td  align="center"><font color=black>4+54=58</font></td></tr><tr><td  align="center"><font color=black>6</font></td><td  align="center"><font color=black>36</font></td><td  align="center"><font color=black>6+36=42</font></td></tr><tr><td  align="center"><font color=black>8</font></td><td  align="center"><font color=black>27</font></td><td  align="center"><font color=black>8+27=35</font></td></tr><tr><td  align="center"><font color=black>9</font></td><td  align="center"><font color=black>24</font></td><td  align="center"><font color=black>9+24=33</font></td></tr><tr><td  align="center"><font color=black>12</font></td><td  align="center"><font color=black>18</font></td><td  align="center"><font color=black>12+18=30</font></td></tr><tr><td  align="center"><font color=black>-1</font></td><td  align="center"><font color=black>-216</font></td><td  align="center"><font color=black>-1+(-216)=-217</font></td></tr><tr><td  align="center"><font color=black>-2</font></td><td  align="center"><font color=black>-108</font></td><td  align="center"><font color=black>-2+(-108)=-110</font></td></tr><tr><td  align="center"><font color=black>-3</font></td><td  align="center"><font color=black>-72</font></td><td  align="center"><font color=black>-3+(-72)=-75</font></td></tr><tr><td  align="center"><font color=black>-4</font></td><td  align="center"><font color=black>-54</font></td><td  align="center"><font color=black>-4+(-54)=-58</font></td></tr><tr><td  align="center"><font color=black>-6</font></td><td  align="center"><font color=black>-36</font></td><td  align="center"><font color=black>-6+(-36)=-42</font></td></tr><tr><td  align="center"><font color=black>-8</font></td><td  align="center"><font color=black>-27</font></td><td  align="center"><font color=black>-8+(-27)=-35</font></td></tr><tr><td  align="center"><font color=black>-9</font></td><td  align="center"><font color=black>-24</font></td><td  align="center"><font color=black>-9+(-24)=-33</font></td></tr><tr><td  align="center"><font color=black>-12</font></td><td  align="center"><font color=black>-18</font></td><td  align="center"><font color=black>-12+(-18)=-30</font></td></tr></table>



From the table, we can see that the two numbers {{{3}}} and {{{72}}} add to {{{75}}} (the middle coefficient).



So the two numbers {{{3}}} and {{{72}}} both multiply to {{{216}}} <font size=4><b>and</b></font> add to {{{75}}}



Now replace the middle term {{{75t}}} with {{{3t+72t}}}. Remember, {{{3}}} and {{{72}}} add to {{{75}}}. So this shows us that {{{3t+72t=75t}}}.



{{{8t^2+highlight(3t+72t)+27}}} Replace the second term {{{75t}}} with {{{3t+72t}}}.



{{{(8t^2+3t)+(72t+27)}}} Group the terms into two pairs.



{{{t(8t+3)+(72t+27)}}} Factor out the GCF {{{t}}} from the first group.



{{{t(8t+3)+9(8t+3)}}} 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.



{{{(t+9)(8t+3)}}} Combine like terms. Or factor out the common term {{{8t+3}}}



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So {{{t^2(8t^2+75t+27)}}} then factors further to {{{t^2(t+9)(8t+3)}}}



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Answer:



So {{{8t^4+75t^3+27t^2}}} completely factors to {{{t^2(t+9)(8t+3)}}}.



In other words, {{{8t^4+75t^3+27t^2=t^2(t+9)(8t+3)}}}.



Note: you can check the answer by expanding {{{t^2(t+9)(8t+3)}}} to get {{{8t^4+75t^3+27t^2}}} or by graphing the original expression and the answer (the two graphs should be identical).


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