document.write( "Question 698729: What is the x-intercept of a parabola with the vertex (-1,80) and the y intercept (0,75) \n" ); document.write( "

Algebra.Com's Answer #431002 by Positive_EV(69) $\"\"$ $\"About$

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Since this parabola has only one y-intercept, it must open either up or down. A parabola that opens up or down can be written in the form $\"y+-+k+=+a%2A%28x-h%29%5E2\"$ . In this form, the vertex is (h, k). So to start, plug in those values:
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\n" ); document.write( "\n" ); document.write( " $\"y+-+80+=+a%2A%28x%2B1%29%5E2\"$
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\n" ); document.write( "\n" ); document.write( "To find a, plug the point of the y-intercept into this equation:
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\n" ); document.write( "\n" ); document.write( " $\"75+-+80+=+a%2A%280%2B1%29%5E2\"$
\n" ); document.write( " $\"-5+=+a\"$
\n" ); document.write( " $\"y+-+80+=+-5%2A%28x%2B1%29%5E2\"$
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\n" ); document.write( "\n" ); document.write( "You can find the x-intercepts (there will be two of them) by setting y = 0 and solving for x:
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\n" ); document.write( "\n" ); document.write( " $\"-80+=+-5%2A%28x%2B1%29%5E2\"$
\n" ); document.write( " $\"16+=+%28x%2B1%29%5E2\"$
\n" ); document.write( " $\"4+=+%28x%2B1%29\"$ or $\"-4+=+%28x%2B1%29\"$
\n" ); document.write( "So x = 3 or x = -5. The x-intercepts are thus (3,0) and (-5,0). \n" ); document.write( "

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