document.write( "Question 336991: been out of school for 25 years. need help solving a basic equation.\r
\n" ); document.write( "\n" ); document.write( "2xsquared + 7x - 15 \n" ); document.write( "

Algebra.Com's Answer #241529 by jim_thompson5910(35256) $\"\"$ $\"About$

You can put this solution on YOUR website!
I assume you want to factor this.\r
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\n" ); document.write( "\n" ); document.write( "Looking at the expression $\"2x%5E2%2B7x-15\"$ , we can see that the first coefficient is $\"2\"$ , the second coefficient is $\"7\"$ , and the last term is $\"-15\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Now multiply the first coefficient $\"2\"$ by the last term $\"-15\"$ to get $\"%282%29%28-15%29=-30\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Now the question is: what two whole numbers multiply to $\"-30\"$ (the previous product) and add to the second coefficient $\"7\"$ ?\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 $\"-30\"$ (the previous product).\r
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\n" ); document.write( "\n" ); document.write( "Factors of $\"-30\"$ :\r
\n" ); document.write( "\n" ); document.write( "1,2,3,5,6,10,15,30\r
\n" ); document.write( "\n" ); document.write( "-1,-2,-3,-5,-6,-10,-15,-30\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 $\"-30\"$ .\r
\n" ); document.write( "\n" ); document.write( "1*(-30) = -30
\n" ); document.write( "2*(-15) = -30
\n" ); document.write( "3*(-10) = -30
\n" ); document.write( "5*(-6) = -30
\n" ); document.write( "(-1)*(30) = -30
\n" ); document.write( "(-2)*(15) = -30
\n" ); document.write( "(-3)*(10) = -30
\n" ); document.write( "(-5)*(6) = -30\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 $\"7\"$ :\r
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First Number	Second Number	Sum
1	-30	1+(-30)=-29
2	-15	2+(-15)=-13
3	-10	3+(-10)=-7
5	-6	5+(-6)=-1
-1	30	-1+30=29
-2	15	-2+15=13
-3	10	-3+10=7
-5	6	-5+6=1

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\n" ); document.write( "\n" ); document.write( "From the table, we can see that the two numbers $\"-3\"$ and $\"10\"$ add to $\"7\"$ (the middle coefficient).\r
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\n" ); document.write( "\n" ); document.write( "So the two numbers $\"-3\"$ and $\"10\"$ both multiply to $\"-30\"$ and add to $\"7\"$ \r
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\n" ); document.write( "\n" ); document.write( "Now replace the middle term $\"7x\"$ with $\"-3x%2B10x\"$ . Remember, $\"-3\"$ and $\"10\"$ add to $\"7\"$ . So this shows us that $\"-3x%2B10x=7x\"$ .\r
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\n" ); document.write( "\n" ); document.write( " $\"2x%5E2%2Bhighlight%28-3x%2B10x%29-15\"$ Replace the second term $\"7x\"$ with $\"-3x%2B10x\"$ .\r
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\n" ); document.write( "\n" ); document.write( " $\"%282x%5E2-3x%29%2B%2810x-15%29\"$ Group the terms into two pairs.\r
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\n" ); document.write( "\n" ); document.write( " $\"x%282x-3%29%2B%2810x-15%29\"$ Factor out the GCF $\"x\"$ from the first group.\r
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\n" ); document.write( "\n" ); document.write( " $\"x%282x-3%29%2B5%282x-3%29\"$ 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( " $\"%28x%2B5%29%282x-3%29\"$ Combine like terms. Or factor out the common term $\"2x-3\"$ \r
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\n" ); document.write( "\n" ); document.write( "Answer:\r
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\n" ); document.write( "\n" ); document.write( "So $\"2x%5E2%2B7x-15\"$ factors to $\"%28x%2B5%29%282x-3%29\"$ .\r
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\n" ); document.write( "\n" ); document.write( "In other words, $\"2x%5E2%2B7x-15=%28x%2B5%29%282x-3%29\"$ .\r
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\n" ); document.write( "\n" ); document.write( "Note: you can check the answer by expanding $\"%28x%2B5%29%282x-3%29\"$ to get $\"2x%5E2%2B7x-15\"$ or by graphing the original expression and the answer (the two graphs should be identical).\r
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\n" ); document.write( "\n" ); document.write( "If you need more help, email me at jim_thompson5910@hotmail.com\r
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\n" ); document.write( "\n" ); document.write( "Also, feel free to check out my website. \r
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\n" ); document.write( "\n" ); document.write( "Jim \n" ); document.write( "

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