document.write( "Question 181708: The question is:
\n" ); document.write( "The number of quadruplet births Q in the United States from 1989 to 1998 can be modeled by $\"Q=+-0.5t%5E3%2B11.7t%5E2-21.5t%2B218.6\"$ , where t represents the number of years since 1989. For what values of t does this model no longer give realistic data? Explain your reasoning.\r
\n" ); document.write( "\n" ); document.write( "I tried to figure it out, but I think I was way off. I just substituted t for different numbers, but went in order (2,3,4). I just don't understand how to solve it. Please help me and explain how you got it, so I don't just copy, but I will also understand how to solve it. \n" ); document.write( "

Algebra.Com's Answer #136335 by Edwin McCravy(20056) $\"\"$ $\"About$

You can put this solution on YOUR website!
The question is:
\n" ); document.write( "The number of quadruplet births Q in the United States from 1989 to 1998 can be modeled by $\"Q=+-0.5t%5E3%2B11.7t%5E2-21.5t%2B218.6\"$ , where t represents the number of years since 1989. For what values of t does this model no longer give realistic data? Explain your reasoning.\r
\n" ); document.write( "\n" ); document.write( "I tried to figure it out, but I think I was way off. I just substituted t for different numbers, but went in order (2,3,4). I just don't understand how to solve it. Please help me and explain how you got it, so I don't just copy, but I will also understand how to solve it.
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document.write( "Edwin's solution:\r\n" );
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document.write( "You'll eventually get the answer that way, but it'll take\r\n" );
document.write( "you a long long time.  Surely your teacher expects you to\r\n" );
document.write( "have a graphing calculator, such as a TI-83 or 84.  You \r\n" );
document.write( "must get one and learn to use it, for this is a graphing \r\n" );
document.write( "calculator problem.\r\n" );
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document.write( "If you have a TI-83 or TI-84\r\n" );
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document.write( "You have to use X instead of t\r\n" );
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document.write( "Press the WINDOW key\r\n" );
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document.write( "Type these values instead of\r\n" );
document.write( "what you find there:\r\n" );
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document.write( "WINDOW\r\n" );
document.write( "Xmin=-1\r\n" );
document.write( "Xmax=25\r\n" );
document.write( "Xscl=1\r\n" );
document.write( "Ymin=-100\r\n" );
document.write( "Ymax=1000\r\n" );
document.write( "Yscl=100\r\n" );
document.write( "Xres=1\r\n" );
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document.write( "Press Y= and enter -.5X^3+11.7X^2-21.5X+218.6 next to \Y1=\r\n" );
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document.write( "so the top line reads \Y1=-.5X^3+11.7X^2-21.5X+218.6 next to \Y1=\r\n" );
document.write( "(it will scroll onto the next line since there's not enough room\r\n" );
document.write( "for it all to fit on one line) \r\n" );
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document.write( "Press GRAPH\r\n" );
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document.write( "You'll see a graph.\r\n" );
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document.write( "Press TRACE\r\n" );
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document.write( "Then use your left and right arrows to trace the\r\n" );
document.write( "curve all the way to the right end.  As you move the\r\n" );
document.write( "cursor along the curve, the x and y coordinates\r\n" );
document.write( "of the point it's on are given at the bottom of the\r\n" );
document.write( "screen, to many decimal places.   \r\n" );
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document.write( "Now when you've mover the cursor to the bottom right of \r\n" );
document.write( "the curve you see that it goes negative when you get to \r\n" );
document.write( "about 22.4. And it is not valid when it goes negative. \r\n" );
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document.write( "When you substitute in 22 you get 84.5, and when you \r\n" );
document.write( "substitute in 23 you get -170.1.\r\n" );
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document.write( "You can even find the value where the curve becomes\r\n" );
document.write( "zero if you know how to use a graphing calculator.   \r\n" );
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document.write( "it is t = 22.351309 years after 1989\r\n" );
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document.write( "So it is no longer valid after 22.351309 years after 1989.\r\n" );
document.write( "By the way, that works out to be May 18, 2011 at 6:24 PM.  \r\n" );
document.write( "That is the instant when there will be 0 quadruplet births \r\n" );
document.write( "according to the modeling formula.\r\n" );
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document.write( "Edwin

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