document.write( "Question 80009: Can you please help me write a quadratic function with this set of data?
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Algebra.Com's Answer #57382 by Edwin McCravy(20086) $\"\"$ $\"About$

You can put this solution on YOUR website!

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document.write( "Can you please help me write a quadratic function \r\n" );
document.write( "with this set of data? \r\n" );
document.write( "(0,254)(4,234)(8,235)(12,239)(16,255) \r\n" );
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document.write( "f(0) = 254\r\n" );
document.write( "f(4) = 234\r\n" );
document.write( "f(8) = 235\r\n" );
document.write( "f(12) = 239\r\n" );
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document.write( "There is a terribly long formula for finding the \r\n" );
document.write( "quadratic regression formula.  When you plug \r\n" );
document.write( "into it you get:\r\n" );
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document.write( "y = f(x) = 75/224x² - 1451/280x + 1769/7 \r\n" );
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document.write( "Are you allowed to use a TI-83 or TI-84?  If so, then\r\n" );
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document.write( "press STAT then ENTER, \r\n" );
document.write( "enter the five x values under L1 and the five values for f(x) in L2.\r\n" );
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document.write( "press STAT then the right arrow then 5, then ENTER\r\n" );
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document.write( "You see:\r\n" );
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document.write( "y = ax²+bx+c\r\n" );
document.write( "a=.3348214286\r\n" );
document.write( "b=-5.182142857\r\n" );
document.write( "c = 252.7142657\r\n" );
document.write( "R²=.9564574654\r\n" );
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document.write( "Since R² is near 1, the fit is good.\r\n" );
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document.write( "plug those values into \r\n" );
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document.write( "y = ax²+bx+c\r\n" );
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document.write( "y = f(x) = .3348214286x² - 5.182142857x + 252.7142857\r\n" );
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document.write( "Here's the graph of that, the o's are your 5 points above:\r\n" );
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document.write( "Edwin

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