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Schoolwork Help Thread

Started by SlowPokemon, April 08, 2011, 07:52:13 AM

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BlackDragonSlayer

When I am in desperate need for help and no one else is there to help, I turn to the people of NSM for aid!


Use the Substitution x = 3sinθ, -pi/2 ≤ θ ≤ pi/2, and the identity cot^2 θ = csc^2 θ - 1 to evaluate

S (sqrt(9 - x^2)/x^2) dx


What I have so far is:
x = 3sinθ

sqrt(9-9sin^2 θ) = sqrt(9(1-sin^2 θ) = sqrt(9 cos^2 θ) = 3cosθ

dx = 3cosθ dθ

And from there, anything I do ends up differing drastically from the answer the book gives (it's an odd-numbered problem; unfortunately, no step-by-step solutions here). There are two more problems like it after, so I think knowing how to do this problem will also help me with those two. I understand trig substitution. I understand that you need to do trig substitution to solve this problem. My problem with this one is that there are absolutely no example problems in the book that vaguely resemble this one in form or complexity, and thus I am lost at how to approach this one.

That "S" is supposed to be an integral sign, by the way.
And the moral of the story: Quit while you're a head.

Fakemon Dex
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Dudeman

#316
What happened to the x^2 on the bottom? Should you be ending up with 3cosθ/9sin^2 θ? Then you can separate that out into 3cosθ/3sinθ * 1/3sinθ and go from there, right?

EDIT: Also given that the problem specifically tells you cot^2 θ = csc^2 θ - 1, the fact that you end up with cosθ/sinθ at some point should be a big hint that there should be a conversion to cot^2 θ somewhere in there. It's been a while since I've done derivatives of periodic functions, but that does stand out to me.
Quote from: braixen1264 on December 03, 2015, 03:52:29 PMDudeman's facial hair is number 1 in my book

BlackDragonSlayer

No, it turns into (3cos(θ))^2 / (3sin (θ))^2 , which would, if I'm correct, would turn to (3cot(θ))^2
And the moral of the story: Quit while you're a head.

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Latios212

My arrangements and YouTube channel!

Quote from: Dudeman on February 22, 2016, 10:16:37 AM
who needs education when you can have WAIFUS!!!!!

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turtle

LeviR.star

Whoa, I didn't know this thread existed. This'll come in handy.

So, there is a set of 4 problems in my math review:

5. Which sets of ordered pairs represent functions from A to B? Explain why or why not.

A = {10, 20, 30, 40} and B = {0, 2, 4, 6}

a. {(20, 4), (40, 0), (20, 6), (30,2)}
b. {(10, 4), (20, 4), (30, 4), (40, 4)}
c. {(40, 0), (30, 2), (20, 4), (10, 6)}
d. {(20, 2), (10,0), (40, 4)}

I don't necessarily need the answers, but I need to know how to perform this type of problem for tomorrow. Thank you to anyone in advance.

Double ninja'd
Check out my Youtube channel for remixes and original music! LeviR.star's Remixes

Also check out my piano arrangements here on my PA thread! LeviR.star's Arrangements

Dudeman

@Levi: Functions only have one output for every input. In other words, the sets of ordered pairs which represent functions are the sets that never repeat an input (that is, the first number in the pair) and get a different output. In this case, that's every answer except a, since a has two outputs for 20 (4 and 6).
Quote from: braixen1264 on December 03, 2015, 03:52:29 PMDudeman's facial hair is number 1 in my book

LeviR.star

Quote from: Dudeman on September 13, 2017, 01:59:11 PM@Levi: Functions only have one output for every input. In other words, the sets of ordered pairs which represent functions are the sets that never repeat an input (that is, the first number in the pair) and get a different output. In this case, that's every answer except a, since a has two outputs for 20 (4 and 6).

You're the best, Dudeman! You explained that better than anyone else I asked today!

Now all I have to do is finish my other homework, practice All-State music and eat a late lunch in time to watch the Direct livestream at 5:00.
Check out my Youtube channel for remixes and original music! LeviR.star's Remixes

Also check out my piano arrangements here on my PA thread! LeviR.star's Arrangements

mastersuperfan

Quote from: NocturneOfShadow on February 11, 2016, 03:00:36 PMthere's also a huge difference in quality between 2000 songs and 2010 songs
Quote from: Latios212 on February 11, 2016, 03:29:24 PMThe difference between 2000 songs and 2010 songs is 10 songs.

Mashi

#323

Dudeman

AGH DAMMIT RIGHT YOU HAVE TO TAKE THE DERIVATIVE OF X TO GET Dθ DAMMIT
Quote from: braixen1264 on December 03, 2015, 03:52:29 PMDudeman's facial hair is number 1 in my book

Zunawe

*cough* integral symbol and d theta at step 5 *cough cough*

Edit: Oh wait, I think I see what you meant. I've never seen anybody do that.
You know you've been playing too much Dragon Quest when you're afraid your Hershey's Kisses are going to flee.

I program things

BlackDragonSlayer

Mashi explained it better than both my professor and the book itself. :P Thank you very much!
And the moral of the story: Quit while you're a head.

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Pianist Da Sootopolis

#327
Hey y'all

So I gotta do a project about Leto/Latona, goddess of modesty and motherhood. Part of this project is a parallel to other cultures; does anyone know of a cultural equivalent in, say, Egyptian, Norse, or other mythologies?
what is shitpost

mikey

#328
My buddy Google knows a lot about Egyptian mythology, lemme go ask him real quick

Edit: he says check out bast, Isis, or taueret
http://www.goddess-guide.com/fertility-goddesses.html
unmotivated

Pianist Da Sootopolis

Quote from: NocturneOfShadow on October 01, 2017, 02:43:35 PMMy buddy Google knows a lot about Egyptian mythology, lemme go ask him real quick

Edit: he says check out bast, Isis, or taueret
http://www.goddess-guide.com/fertility-goddesses.html

Well here I go, searching the web for Isis.
what is shitpost