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  • (January 12, 2023, 01:18:11 AM)

Author Topic: A Maths Question  (Read 1960 times)

Odd_Bloke

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A Maths Question
« on: June 01, 2006, 06:22:00 PM »
I dunno if we have any Maths geeks here but I could really use a hand with this. I'm doing some revision for an upcoming Maths exam. I'm trying to find the differential of 'inverse tanh of sin x'. The answer is supposed to be 'sec x', but I get 'sec squared x'. You can follow my working here (which also makes it much easier to understand the problem in the first place).

Thanks,
Dan
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sociald1077

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Re: A Maths Question
« Reply #1 on: June 01, 2006, 07:21:49 PM »
 :?
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TeraHammer

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Re: A Maths Question
« Reply #2 on: June 01, 2006, 07:28:04 PM »
I don't remember the name of the rule, but you cannot simply substitute sin(x) into x. You have to multiply that equation with the d/dx sin(x) which is cos(x), which makes the solution 1/cos(x).

The general rule goes: d/dx (f(g)) = df/dg * dg/dx. With f = tanh-1(x) and g = sin(x).
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Odd_Bloke

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Re: A Maths Question
« Reply #3 on: June 01, 2006, 09:16:56 PM »
Quote from: TeraHammer on June 01, 2006, 07:28:04 PM
The general rule goes: d/dx (f(g)) = df/dg * dg/dx. With f = tanh-1(x) and g = sin(x).
Oh goodness... I'd forgotten the chain rule... The chain rule!

*goes white-faced and passes out*
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hackess

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Re: A Maths Question
« Reply #4 on: June 01, 2006, 09:34:32 PM »
*waits for Detta to arrive and whip out the maths smarts*
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Min

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Re: A Maths Question
« Reply #5 on: June 02, 2006, 10:33:34 AM »
Looks like Terrahammer did an adequate job of busting out the math smarts.  I probably would have had to look that up anyway.
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ivan

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Re: A Maths Question
« Reply #6 on: June 02, 2006, 11:08:29 AM »
As much as I tried to hate TeraHammer's living guts, I just can't. Dutch + math-head = total coolness, even if he does hate the car I drive.
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TeraHammer

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Re: A Maths Question
« Reply #7 on: June 03, 2006, 08:28:50 AM »
Ah yes, the chain rule, that's what it's called. 8-)

And Ivan, thanks, bugger :lol:
« Last Edit: June 03, 2006, 08:31:55 AM by TeraHammer »
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