document.write( "Question 254065: what is the value of x using the equation \"x%5E2%2B4x-21=0\" \n" ); document.write( "
Algebra.Com's Answer #186373 by richwmiller(17219)\"\" \"About 
You can put this solution on YOUR website!
x^2+4x-21=0 is a quadratic equation.
\n" ); document.write( "It can be factored into
\n" ); document.write( "(x-3)(x+7)=0
\n" ); document.write( "so that its solutions (roots ) are 3 and -7
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Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation \"ax%5E2%2Bbx%2Bc=0\" (in our case \"1x%5E2%2B4x%2B-21+=+0\") has the following solutons:
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\n" ); document.write( " \"x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca\"
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\n" ); document.write( " For these solutions to exist, the discriminant \"b%5E2-4ac\" should not be a negative number.
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\n" ); document.write( " First, we need to compute the discriminant \"b%5E2-4ac\": \"b%5E2-4ac=%284%29%5E2-4%2A1%2A-21=100\".
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\n" ); document.write( " Discriminant d=100 is greater than zero. That means that there are two solutions: \"+x%5B12%5D+=+%28-4%2B-sqrt%28+100+%29%29%2F2%5Ca\".
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\n" ); document.write( " \"x%5B1%5D+=+%28-%284%29%2Bsqrt%28+100+%29%29%2F2%5C1+=+3\"
\n" ); document.write( " \"x%5B2%5D+=+%28-%284%29-sqrt%28+100+%29%29%2F2%5C1+=+-7\"
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\n" ); document.write( " Quadratic expression \"1x%5E2%2B4x%2B-21\" can be factored:
\n" ); document.write( " \"1x%5E2%2B4x%2B-21+=+1%28x-3%29%2A%28x--7%29\"
\n" ); document.write( " Again, the answer is: 3, -7.\n" ); document.write( "Here's your graph:
\n" ); document.write( "\"graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B4%2Ax%2B-21+%29\"
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