Mathematics desk | ||
---|---|---|
< January 2 | << Dec | January | Feb >> | January 4 > |
Welcome to the Wikipedia Mathematics Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
I'm trying to solve this:
dy/dx = 4x + 4x/sqrt(16-x^2)
I figured,
y = ∫(4x + 4x/sqrt(16-x^2))dx
y = 2x^2 + ∫4x(16-x^2)^(-1/2)dx
y = 2x^2 + ∫(64x-4x^3)^(-1/2)dx
let u = 64x-4x^3 <-- But I don't know how to isolate x from here so that I can express x in terms of u.
du = (64-12x^2)dx
dx = du/(-12x^2+64)
So I'm stuck here:
y = 2x^2 + ∫u^(-1/2)(du/(-12x^2+64))dx
How do I isolate that x so that I can substitute for it in terms of u and finish the integration?
Thanks!
--anon —Preceding unsigned comment added by 70.23.86.90 ( talk) 04:46, 3 January 2008 (UTC)
An accounting population consists of 100 accounts, 75 correct and 25 wrong. If 12 accounts are chosen at random, find the probability that at least one account is in error.
Would I be right in saying the answer to this question is
136.206.1.17 ( talk)
Okay than would it be
1-((25!/100!)*(88!/13!))
If its not could somone tell me the answer and why its like that. This isnt a homework question by the way, i'm trying to understand it for an exam. 136.206.1.17 ( talk) 10:30, 4 January 2008 (UTC)
As I have just been told off by ConMan for volunteering to give you the answer I will just give you a BIG clue. The probabaility that the first one is correct is , the probability that the second one is correct is etcetera. Multiply together all 12 of those, express it in factorials and subtract from one. You should now be able to see what is wrong with your expression. SpinningSpark 17:36, 5 January 2008 (UTC)
The article on numeral systems mentions that the only reason we use a system with ten bases is because we happen to have five fingers on each hand. Although the article mentions systems using different bases (five, eight, even sixty!), I didn't see one that uses the mathematical constant e. Does such a system exist? If not, would it be possible and/or useful?
Mikmd ( talk) 22:18, 3 January 2008 (UTC)
Mathematics desk | ||
---|---|---|
< January 2 | << Dec | January | Feb >> | January 4 > |
Welcome to the Wikipedia Mathematics Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
I'm trying to solve this:
dy/dx = 4x + 4x/sqrt(16-x^2)
I figured,
y = ∫(4x + 4x/sqrt(16-x^2))dx
y = 2x^2 + ∫4x(16-x^2)^(-1/2)dx
y = 2x^2 + ∫(64x-4x^3)^(-1/2)dx
let u = 64x-4x^3 <-- But I don't know how to isolate x from here so that I can express x in terms of u.
du = (64-12x^2)dx
dx = du/(-12x^2+64)
So I'm stuck here:
y = 2x^2 + ∫u^(-1/2)(du/(-12x^2+64))dx
How do I isolate that x so that I can substitute for it in terms of u and finish the integration?
Thanks!
--anon —Preceding unsigned comment added by 70.23.86.90 ( talk) 04:46, 3 January 2008 (UTC)
An accounting population consists of 100 accounts, 75 correct and 25 wrong. If 12 accounts are chosen at random, find the probability that at least one account is in error.
Would I be right in saying the answer to this question is
136.206.1.17 ( talk)
Okay than would it be
1-((25!/100!)*(88!/13!))
If its not could somone tell me the answer and why its like that. This isnt a homework question by the way, i'm trying to understand it for an exam. 136.206.1.17 ( talk) 10:30, 4 January 2008 (UTC)
As I have just been told off by ConMan for volunteering to give you the answer I will just give you a BIG clue. The probabaility that the first one is correct is , the probability that the second one is correct is etcetera. Multiply together all 12 of those, express it in factorials and subtract from one. You should now be able to see what is wrong with your expression. SpinningSpark 17:36, 5 January 2008 (UTC)
The article on numeral systems mentions that the only reason we use a system with ten bases is because we happen to have five fingers on each hand. Although the article mentions systems using different bases (five, eight, even sixty!), I didn't see one that uses the mathematical constant e. Does such a system exist? If not, would it be possible and/or useful?
Mikmd ( talk) 22:18, 3 January 2008 (UTC)