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Topic: L'Hopital Rules, Oh Never Mind... (Read 728 times) |
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ThudnBlunder
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L'Hopital Rules, Oh Never Mind...
« on: Aug 20th, 2010, 7:53pm » |
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2x + sin2x
What is LIM ----------- ?
x   xsinx + cosx
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| « Last Edit: Aug 23rd, 2010, 2:08pm by ThudnBlunder » |
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Noke Lieu
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Re: L'Hopital Rules, Oh Never Mind...
« Reply #1 on: Aug 23rd, 2010, 6:49pm » |
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oh. Right.
d(2x + sin2x)/dx 2+ cos x
------------------ = ----------
d(xsinx + cosx)/dx x cos x
and then I get a bit wobbly, frankly. It's been a long time between calculus exams for me... 
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ThudnBlunder
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Re: L'Hopital Rules, Oh Never Mind...
« Reply #2 on: Aug 23rd, 2010, 6:56pm » |
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http://calc.matthen.com/
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towr
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Re: L'Hopital Rules, Oh Never Mind...
« Reply #3 on: Aug 24th, 2010, 1:18am » |
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I'm not sure what you're asking; the expression you give has no limit at infinity.
If you try x = 2 pi k and x = 2 pi k + pi/2, for integer k, the fraction yields 4 pi k and 2 respectively, so it alternates between values indefinitely.
Or are you asking for the limit at the wrong point? If you want us to apply L'Hopital, it should be at a point where the denominator and numerator are both 0. But that doesn't seem to happen at the same time for any x either.
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| « Last Edit: Aug 24th, 2010, 1:21am by towr » |
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Wikipedia, Google, Mathworld, Integer sequence DB
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ThudnBlunder
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Re: L'Hopital Rules, Oh Never Mind...
« Reply #4 on: Aug 24th, 2010, 1:46am » |
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on Aug 24th, 2010, 1:18am, towr wrote:| I'm not sure what you're asking; the expression you give has no limit at infinity.. |
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That's right, but straightforward application of L'Hopital gives an answer of zero. It's called a trick question, duh.
Your query is like a passing fish popping its head out of the water and asking an angler, "What are you sitting there for?", before swimming off unconcernedly. LOL As it says in the title, oh never mind...
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| « Last Edit: Aug 24th, 2010, 3:52am by ThudnBlunder » |
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