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Topic: True/False?
Replies: 4   Last Post: Sep 7, 1999 12:28 PM

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Peter Percival

Posts: 95
Registered: 12/8/04
Re: True/False?
Posted: Sep 6, 1999 2:59 PM
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If the range of t is bounded above and below then there is such a
polynomial by the Weierstrass Approximation Theorem. If t is allowed to
be indefinitely large, positive or negative, then there is not for the
reason you note. wrote:

> True or False? :
> There exists a polynomial P such that:
> | P(t) - cos(t) | <= 10^-6.
> |t|, meaning the absolute value of t.
> I said false. Because P(t) could be very large. Then cos(t) is
> comparatively small. Then the answer is a large positive number,
> greater than 10^-6.
> Although then I started to think along the lines of the Taylor series,
> because
> cos(t) = 1 - x^2/2! + x^4/4! - x^6/6! + ...
> and this is valid for all values of t, so perhaps there could be a
> polynomial (I'm not sure what that would be).
> So on the other hand it could also be true. Which is the correct
> answer?

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