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Author Topic: Mathematics Help Thread  (Read 226877 times)

MagmaMcFry

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Re: Mathematics Help Thread
« Reply #2190 on: June 05, 2016, 04:34:12 pm »

Say you fill up your card with x cents each time and a coffee costs y cents. After x coffees, you will have filled up your card exactly y times.
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Arx

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Re: Mathematics Help Thread
« Reply #2191 on: June 06, 2016, 07:48:12 am »

The way sigma notation works is that if you have a sequence of things x1, x2, ... , xn, Σni=1 (xi) is the sum of the terms x1 to xn. i is used to denote the 'index'.

So Σ5i=1 (xi) = x1 + x2 + x3 + x4 + x5.

If you program at all, think of it as like a for loop:

for i = 1:n
    sum = sum + xi

This may shed some light on the mean deviation formula.
« Last Edit: June 06, 2016, 07:49:58 am by Arx »
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Arx

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Re: Mathematics Help Thread
« Reply #2192 on: June 06, 2016, 08:17:01 am »

For future reference, x bar (x̄) is the standard notation for a mean. Every now and then some special snowflake decides to use another, but in every serious and/or scientific context I've seen it's been x bar.
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RedWarrior0

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Re: Mathematics Help Thread
« Reply #2193 on: June 07, 2016, 10:25:55 am »

More specifically, it's the mean of the sample. In most real world contexts this will be the only mean you have access to, but there's also the mean of the entire population, and that would be mu.
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3man75

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Re: Mathematics Help Thread
« Reply #2194 on: July 26, 2016, 09:03:58 pm »

Hi guys I need help calculating my grades to give me an idea of what I should do in my upcoming final.

My grade is broken down currently to be 30% H.W and 50% tests (total possible grade) initially. Then my professor says that this is false and that they should both be 40% each and it will be changed...when he gets around to it.

I have 28.86 out of 30 points for h.w and 34.56 points out of 50 points in my tests. After the weight changes are done what will be my new total?

Average scores are 96.19% for H.W and 69.1% Tests.

63.41 points out of 80 points.

Basically, as minor as it might be I'm trying to have at least 75% of the total grade because of how the class is setup. I think he may be curbing the grades but i'm not sure if he is or by how much (He goes back and forth from being hardass to 'I'm old and I don't care. Just pass').

How do I convert these scores?
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hops

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Re: Mathematics Help Thread
« Reply #2195 on: September 09, 2016, 10:00:19 am »

Can someone explain to me how u-substitution integration works?
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hops

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Re: Mathematics Help Thread
« Reply #2196 on: September 09, 2016, 10:07:28 am »

Well I mean kind of like a pure mathematical proof and basis. And I don't understand how the substitution is equivalent with the reverse chain rule.
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hops

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Re: Mathematics Help Thread
« Reply #2197 on: September 09, 2016, 10:33:53 am »

But how do you go from that to ∫f(g(x)) dx = g'(x)-1*∫f(u) du where g(x) = u though.

aaaaa
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TheDarkStar

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Re: Mathematics Help Thread
« Reply #2198 on: September 09, 2016, 10:46:56 am »

But how do you go from that to ∫f(g(x)) dx = g'(x)-1*∫f(u) du where g(x) = u though.

aaaaa

The chain rule says (f(g(x)))' = f'(g(x))g'(x). With u substitution, you just rename g'(x) as u because u is easy to write and it's easy to see what's going on: ∫f'(g(x))g'(x)dx = ∫f'(u)u'dx, and then you find what du is and manipulate the expression so that you obtain it somewhere. You end up with ∫f'(u)du, which is just integrating whatever f(u) is.

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Re: Mathematics Help Thread
« Reply #2199 on: September 11, 2016, 05:51:58 am »

Is there any way to integrate f(x)=a/(a-x) in term of x?
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Arx

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Re: Mathematics Help Thread
« Reply #2200 on: September 11, 2016, 05:56:42 am »

It's equivalent to a∫1/(a-x)dx, which integrates to ln(a-x). so aln(a-x).

Assuming a is a constant.
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Re: Mathematics Help Thread
« Reply #2201 on: September 11, 2016, 05:58:04 am »

Oh, right.
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Arx

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Re: Mathematics Help Thread
« Reply #2202 on: September 11, 2016, 06:02:32 am »

I get caught by missing that stuff way too often...
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Baffler

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Re: Mathematics Help Thread
« Reply #2203 on: September 11, 2016, 06:54:49 pm »

I need to "demonstrate how to find the surface area, area, and final position of an arbitrary object moving in four dimensions." There aren't any numbers associated with the problem, he just wants us to show it worked out. I'm really not sure how to approach the problem, but that's my entire test tomorrow.
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MagmaMcFry

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Re: Mathematics Help Thread
« Reply #2204 on: September 11, 2016, 07:03:29 pm »

I need to "demonstrate how to find the surface area, area, and final position of an arbitrary object moving in four dimensions." There aren't any numbers associated with the problem, he just wants us to show it worked out. I'm really not sure how to approach the problem, but that's my entire test tomorrow.

How to find the surface area depends on how the given object is described. How to find the final position depends on in what form the motion is given. If the question isn't any more specific than what you've quoted, then there is literally nothing more to say. If he wants more details, tell him you too need more details, and you can't read minds.

Although if you're a smartass you could just wait for the object to finish moving and then check its shirt size.
« Last Edit: September 11, 2016, 07:05:41 pm by MagmaMcFry »
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