document.write( "Question 707391: 9r^2-30r+25 \n" ); document.write( "

Algebra.Com's Answer #435676 by jim_thompson5910(35256) $\"\"$ $\"About$

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\n" ); document.write( "\n" ); document.write( "Looking at the expression $\"9r%5E2-30r%2B25\"$ , we can see that the first coefficient is $\"9\"$ , the second coefficient is $\"-30\"$ , and the last term is $\"25\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Now multiply the first coefficient $\"9\"$ by the last term $\"25\"$ to get $\"%289%29%2825%29=225\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Now the question is: what two whole numbers multiply to $\"225\"$ (the previous product) and add to the second coefficient $\"-30\"$ ?\r
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\n" ); document.write( "\n" ); document.write( "To find these two numbers, we need to list all of the factors of $\"225\"$ (the previous product).\r
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\n" ); document.write( "\n" ); document.write( "Factors of $\"225\"$ :\r
\n" ); document.write( "\n" ); document.write( "1,3,5,9,15,25,45,75,225\r
\n" ); document.write( "\n" ); document.write( "-1,-3,-5,-9,-15,-25,-45,-75,-225\r
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\n" ); document.write( "\n" ); document.write( "Note: list the negative of each factor. This will allow us to find all possible combinations.\r
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\n" ); document.write( "\n" ); document.write( "These factors pair up and multiply to $\"225\"$ .\r
\n" ); document.write( "\n" ); document.write( "1*225 = 225
\n" ); document.write( "3*75 = 225
\n" ); document.write( "5*45 = 225
\n" ); document.write( "9*25 = 225
\n" ); document.write( "15*15 = 225
\n" ); document.write( "(-1)*(-225) = 225
\n" ); document.write( "(-3)*(-75) = 225
\n" ); document.write( "(-5)*(-45) = 225
\n" ); document.write( "(-9)*(-25) = 225
\n" ); document.write( "(-15)*(-15) = 225\r
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\n" ); document.write( "\n" ); document.write( "Now let's add up each pair of factors to see if one pair adds to the middle coefficient $\"-30\"$ :\r
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First Number	Second Number	Sum
1	225	1+225=226
3	75	3+75=78
5	45	5+45=50
9	25	9+25=34
15	15	15+15=30
-1	-225	-1+(-225)=-226
-3	-75	-3+(-75)=-78
-5	-45	-5+(-45)=-50
-9	-25	-9+(-25)=-34
-15	-15	-15+(-15)=-30

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\n" ); document.write( "\n" ); document.write( "From the table, we can see that the two numbers $\"-15\"$ and $\"-15\"$ add to $\"-30\"$ (the middle coefficient).\r
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\n" ); document.write( "\n" ); document.write( "So the two numbers $\"-15\"$ and $\"-15\"$ both multiply to $\"225\"$ and add to $\"-30\"$ \r
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\n" ); document.write( "\n" ); document.write( "Now replace the middle term $\"-30r\"$ with $\"-15r-15r\"$ . Remember, $\"-15\"$ and $\"-15\"$ add to $\"-30\"$ . So this shows us that $\"-15r-15r=-30r\"$ .\r
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\n" ); document.write( "\n" ); document.write( " $\"9r%5E2%2Bhighlight%28-15r-15r%29%2B25\"$ Replace the second term $\"-30r\"$ with $\"-15r-15r\"$ .\r
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\n" ); document.write( "\n" ); document.write( " $\"%289r%5E2-15r%29%2B%28-15r%2B25%29\"$ Group the terms into two pairs.\r
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\n" ); document.write( "\n" ); document.write( " $\"3r%283r-5%29%2B%28-15r%2B25%29\"$ Factor out the GCF $\"3r\"$ from the first group.\r
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\n" ); document.write( "\n" ); document.write( " $\"3r%283r-5%29-5%283r-5%29\"$ Factor out $\"5\"$ 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.\r
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\n" ); document.write( "\n" ); document.write( " $\"%283r-5%29%283r-5%29\"$ Combine like terms. Or factor out the common term $\"3r-5\"$ \r
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\n" ); document.write( "\n" ); document.write( " $\"%283r-5%29%5E2\"$ Condense the terms.\r
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\n" ); document.write( "\n" ); document.write( "Answer:\r
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\n" ); document.write( "\n" ); document.write( "So $\"9r%5E2-30r%2B25\"$ factors to $\"%283r-5%29%5E2\"$ .\r
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\n" ); document.write( "\n" ); document.write( "In other words, $\"9r%5E2-30r%2B25=%283r-5%29%5E2\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Note: you can check the answer by expanding $\"%283r-5%29%5E2\"$ to get $\"9r%5E2-30r%2B25\"$ or by graphing the original expression and the answer (the two graphs should be identical).
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