How can I determine the end behavior of a polynomial based on Taylor series?












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I know this represents the cos(x) function, but what does it mean that the summation starts with 1 and ends with 21?



This question is for my review sheet for an exam I have. Also, if I were to write the last three terms, does that mean they would be $x^6/6!, x^8/8!$, and $x^{10}/10!$ ?










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  • $begingroup$
    Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
    $endgroup$
    – Matti P.
    Jan 24 at 10:16








  • 1




    $begingroup$
    The last term is $-x^{42}/42!$, not $x^{10}/10!$
    $endgroup$
    – TonyK
    Jan 24 at 10:22


















0












$begingroup$




I know this represents the cos(x) function, but what does it mean that the summation starts with 1 and ends with 21?



This question is for my review sheet for an exam I have. Also, if I were to write the last three terms, does that mean they would be $x^6/6!, x^8/8!$, and $x^{10}/10!$ ?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
    $endgroup$
    – Matti P.
    Jan 24 at 10:16








  • 1




    $begingroup$
    The last term is $-x^{42}/42!$, not $x^{10}/10!$
    $endgroup$
    – TonyK
    Jan 24 at 10:22
















0












0








0





$begingroup$




I know this represents the cos(x) function, but what does it mean that the summation starts with 1 and ends with 21?



This question is for my review sheet for an exam I have. Also, if I were to write the last three terms, does that mean they would be $x^6/6!, x^8/8!$, and $x^{10}/10!$ ?










share|cite|improve this question











$endgroup$






I know this represents the cos(x) function, but what does it mean that the summation starts with 1 and ends with 21?



This question is for my review sheet for an exam I have. Also, if I were to write the last three terms, does that mean they would be $x^6/6!, x^8/8!$, and $x^{10}/10!$ ?







algebra-precalculus taylor-expansion






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share|cite|improve this question








edited Jan 24 at 18:31









J. W. Tanner

3,2801320




3,2801320










asked Jan 24 at 10:10









user8358234user8358234

342110




342110












  • $begingroup$
    Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
    $endgroup$
    – Matti P.
    Jan 24 at 10:16








  • 1




    $begingroup$
    The last term is $-x^{42}/42!$, not $x^{10}/10!$
    $endgroup$
    – TonyK
    Jan 24 at 10:22




















  • $begingroup$
    Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
    $endgroup$
    – Matti P.
    Jan 24 at 10:16








  • 1




    $begingroup$
    The last term is $-x^{42}/42!$, not $x^{10}/10!$
    $endgroup$
    – TonyK
    Jan 24 at 10:22


















$begingroup$
Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
$endgroup$
– Matti P.
Jan 24 at 10:16






$begingroup$
Is it implied that we are looking at $x to infty$? In that case, you can just look at the last (=highest) term of the polynomial.
$endgroup$
– Matti P.
Jan 24 at 10:16






1




1




$begingroup$
The last term is $-x^{42}/42!$, not $x^{10}/10!$
$endgroup$
– TonyK
Jan 24 at 10:22






$begingroup$
The last term is $-x^{42}/42!$, not $x^{10}/10!$
$endgroup$
– TonyK
Jan 24 at 10:22












1 Answer
1






active

oldest

votes


















0












$begingroup$

If you truncate a Taylor series to a polynomial, you get something that's a good approximation of the function ... if you're close enough. For larger $x$, the fact that it's just a polynomial takes over, and it separates from the function completely to do its own thing. Since it's a polynomial, that thing is to go to $pminfty$ as $xtoinfty$ or $xto -infty$. Which sign? That depends on the sign of the coefficient of the largest-degree term and whether that degree is even or odd.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    so if it is even then sign is positive and if it is odd then sign is negative?
    $endgroup$
    – user8358234
    Jan 24 at 10:29










  • $begingroup$
    Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
    $endgroup$
    – jmerry
    Jan 24 at 10:46










  • $begingroup$
    how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
    $endgroup$
    – user8358234
    Jan 24 at 11:07











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1 Answer
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active

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1 Answer
1






active

oldest

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active

oldest

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active

oldest

votes









0












$begingroup$

If you truncate a Taylor series to a polynomial, you get something that's a good approximation of the function ... if you're close enough. For larger $x$, the fact that it's just a polynomial takes over, and it separates from the function completely to do its own thing. Since it's a polynomial, that thing is to go to $pminfty$ as $xtoinfty$ or $xto -infty$. Which sign? That depends on the sign of the coefficient of the largest-degree term and whether that degree is even or odd.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    so if it is even then sign is positive and if it is odd then sign is negative?
    $endgroup$
    – user8358234
    Jan 24 at 10:29










  • $begingroup$
    Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
    $endgroup$
    – jmerry
    Jan 24 at 10:46










  • $begingroup$
    how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
    $endgroup$
    – user8358234
    Jan 24 at 11:07
















0












$begingroup$

If you truncate a Taylor series to a polynomial, you get something that's a good approximation of the function ... if you're close enough. For larger $x$, the fact that it's just a polynomial takes over, and it separates from the function completely to do its own thing. Since it's a polynomial, that thing is to go to $pminfty$ as $xtoinfty$ or $xto -infty$. Which sign? That depends on the sign of the coefficient of the largest-degree term and whether that degree is even or odd.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    so if it is even then sign is positive and if it is odd then sign is negative?
    $endgroup$
    – user8358234
    Jan 24 at 10:29










  • $begingroup$
    Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
    $endgroup$
    – jmerry
    Jan 24 at 10:46










  • $begingroup$
    how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
    $endgroup$
    – user8358234
    Jan 24 at 11:07














0












0








0





$begingroup$

If you truncate a Taylor series to a polynomial, you get something that's a good approximation of the function ... if you're close enough. For larger $x$, the fact that it's just a polynomial takes over, and it separates from the function completely to do its own thing. Since it's a polynomial, that thing is to go to $pminfty$ as $xtoinfty$ or $xto -infty$. Which sign? That depends on the sign of the coefficient of the largest-degree term and whether that degree is even or odd.






share|cite|improve this answer









$endgroup$



If you truncate a Taylor series to a polynomial, you get something that's a good approximation of the function ... if you're close enough. For larger $x$, the fact that it's just a polynomial takes over, and it separates from the function completely to do its own thing. Since it's a polynomial, that thing is to go to $pminfty$ as $xtoinfty$ or $xto -infty$. Which sign? That depends on the sign of the coefficient of the largest-degree term and whether that degree is even or odd.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Jan 24 at 10:18









jmerryjmerry

14.4k1629




14.4k1629












  • $begingroup$
    so if it is even then sign is positive and if it is odd then sign is negative?
    $endgroup$
    – user8358234
    Jan 24 at 10:29










  • $begingroup$
    Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
    $endgroup$
    – jmerry
    Jan 24 at 10:46










  • $begingroup$
    how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
    $endgroup$
    – user8358234
    Jan 24 at 11:07


















  • $begingroup$
    so if it is even then sign is positive and if it is odd then sign is negative?
    $endgroup$
    – user8358234
    Jan 24 at 10:29










  • $begingroup$
    Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
    $endgroup$
    – jmerry
    Jan 24 at 10:46










  • $begingroup$
    how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
    $endgroup$
    – user8358234
    Jan 24 at 11:07
















$begingroup$
so if it is even then sign is positive and if it is odd then sign is negative?
$endgroup$
– user8358234
Jan 24 at 10:29




$begingroup$
so if it is even then sign is positive and if it is odd then sign is negative?
$endgroup$
– user8358234
Jan 24 at 10:29












$begingroup$
Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
$endgroup$
– jmerry
Jan 24 at 10:46




$begingroup$
Since you haven't specified what "it" is, out of several possible parameters, I can't answer your question. Or, for that matter, what "sign" refers to.
$endgroup$
– jmerry
Jan 24 at 10:46












$begingroup$
how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
$endgroup$
– user8358234
Jan 24 at 11:07




$begingroup$
how does the summation from 1 to 21 affect the way the polynomial behaves? how it rises and falls? and how would i write the last three terms of this polynomial?
$endgroup$
– user8358234
Jan 24 at 11:07


















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