Homework Help Thread

2011-01-05 00:47:20

#576

mcminty: Moderating your content for the Australian Govt.; +879|6745|Sydney, Australia

You know, this is more a statistics/hypothesis testing/analysis of variance thing, but it would be interesting to see some X-Y scatter plots of paired variables.. It wouldn't be too hard at all if you have this all in a spreadsheet

If any of the plots are approximately linear, then it means one of the variables isn't actually needed...

2011-01-26 01:55:02

#577

nukchebi0: Пушкин, наше всё; +387|6348|New Haven, CT

Yo necesito un poco ayudo, por favor.

I have a problem wherein I need to calculate the variance of a bond that has a .45 probability of paying 100, .3 probability of paying 80, and .25 of paying 20. Do I treat each value as one separate and equal entity, for a mean of 66.7, or do I weigh them based on their probabilities of occurring?

2011-01-26 02:04:22

#578

AussieReaper: ( ͡° ͜ʖ ͡°); +5,761|6177|what

Weigh them based on their probabilities of occuring.

2011-01-26 02:15:08

#579

nukchebi0: Пушкин, наше всё; +387|6348|New Haven, CT

So the mean is the same thing as the expected value?

2011-01-26 02:29:27

#580

AussieReaper: ( ͡° ͜ʖ ͡°); +5,761|6177|what

The average isn't really the expected value though, is it?

The bond might not pay 66.7 and only values 100, 80 and 20. etc

2011-01-26 03:01:50

#581

nukchebi0: Пушкин, наше всё; +387|6348|New Haven, CT

Expected value is the sum of p_ix_i. Isn't that exactly how you told me to calculate the mean?

2011-02-08 14:10:32

#582

Hurricane2k9: Pendulous Sweaty Balls; +1,538|5726|College Park, MD

The height of a rocket launched form the ground is given by the function s(t)=-16t^2+90t
S is height above ground in feet, t is time

The rocket is 60 feet above the ground at which times?

So I set it = to 60:

60=-16t^2+90t
or
0=-16t^2+90t-60

But then if you solve for t you get some fucked up numbers (at least according to WolframAlpha), numbers that WebAssign says are wrong. What do?

Nevermind, figured it out, I mistyped something

Last edited by Hurricane2k9 (2011-02-08 14:14:16)

https://static.bf2s.com/files/user/36793/marylandsig.jpg

2011-02-19 14:56:29

#583

nukchebi0: Пушкин, наше всё; +387|6348|New Haven, CT

What is the junction depth in semiconductor doping?

2011-02-19 15:40:24

#584

m3thod: All kiiiiiiiiinds of gainz; +2,197|6695|UK

Easy, I think you'll find the answer to be the following:

\_/
\_/ X ------ = c[_]
\_/

Last edited by m3thod (2011-02-19 15:42:19)

Blackbelts are just whitebelts who have never quit.

2011-02-28 17:32:54

#585

Bevo: Nah; +718|6545|Austin, Texas

Anyone here decent with matrices? I could really use some help with some (applied) matrices questions.

I'm to determine the jacobian of a matrix for a 2d planar robot who's position is a function of x, y, and theta. 3 limbs, should be a 3x3 jacobian. I took partials of x across the first row with respect to theta 1, 2, and 3, and then y for the second row, and theta for the last row. Not getting the same result as finding the position by hand, not even close..

Karma and love for help. Exam soon.

2011-03-01 00:14:52

#586

nukchebi0: Пушкин, наше всё; +387|6348|New Haven, CT

Здесь: http://www.math.ucla.edu/~ronmiech/Calc … 886_5.html

2011-03-08 14:54:44

#587

Hurricane2k9: Pendulous Sweaty Balls; +1,538|5726|College Park, MD

Can someone help with this?
Simplify:
3^5x * 27^3x-1

to the form: 3^Ax+b = 3^c * 3^Dx

I know exponent properties and all that, and I got what I thought was the right answer, but it wasn't. I made 27 be (3³)^3x-1, then multiplied the ^3 by 3x-1 and went from there but obviously that's not right.

Last edited by Hurricane2k9 (2011-03-08 15:27:00)

2011-03-08 18:32:18

#588

SenorToenails: Veritas et Scientia; +444|6154|North Tonawanda, NY

3^5x*27^3x-1 = 3^5x*(3³)^3x-1 = 3^5x*3^9x-3 = 3^14x-3 = 3^14x*3^-3

I didn't have any paper handy...but that seems right to me! I'm not sure about what form you need it in, unless you need multiple forms of the equality OR (as I assume) you imply that A = D = 14 and b = c = -3.

2011-03-08 18:40:26

#589

Hurricane2k9: Pendulous Sweaty Balls; +1,538|5726|College Park, MD

yeah, it's embarrassing, but I changed the 27 to 3^9... caught it a few hours ago but thanks any way!

2011-03-08 19:09:22

#590

SenorToenails: Veritas et Scientia; +444|6154|North Tonawanda, NY

Hurricane2k9 wrote:
yeah, it's embarrassing, but I changed the 27 to 3^9... caught it a few hours ago but thanks any way!

haha, shit happens! Your university may have a site license or computers with Mathematica available...you can use it to perform symbolic algebraic manipulations like this with the Simplify[...] or FullSimplify[...] commands. It can be handy to check your work or help you out when stuck.

2011-03-08 19:10:38

#591

Hurricane2k9: Pendulous Sweaty Balls; +1,538|5726|College Park, MD

I've been using WolframAlpha plenty! Although even if I tell it to differentiate or simplify, I still try to figure out how it actually gets there.

2011-03-15 10:21:59

#592

Stimey: +786|6144|Ontario | Canada

$https://static.bf2s.com/files/user/31122/math.png$

2011-03-15 10:26:44

#593

Stimey: +786|6144|Ontario | Canada

nvm I can just transpose then its simple

2011-03-15 10:50:41

#594

Stimey: +786|6144|Ontario | Canada

nvm2.0 dont even have to rofl

2011-03-15 10:55:25

#595

Stimey: +786|6144|Ontario | Canada

wow just watched a youtube video that explained this 10000x better than my teacher

this is babies now

2011-03-15 10:59:41

#596

presidentsheep: Back to the Fuhrer; +208|5985|Places 'n such

Matrices? Khan Academy do a decent series of lectures/videos on them:

http://www.khanacademy.org/video/introd … %20Algebra

I'd type my pc specs out all fancy again but teh mods would remove it. Again.

2011-03-15 11:22:52

#597

Stimey: +786|6144|Ontario | Canada

http://www.youtube.com/watch?v=sYlOjyPy … re=related

Thats the video I watched. He actually has a whole series too.
You should see the way they have it printed in my textbook, very difficult to grasp.
This guy just says `Dot product of the first row with the first column` and I was like `Oh, this all makes so much more sense`

2011-04-30 18:15:22

#598

Bevo: Nah; +718|6545|Austin, Texas

Shot in the dark, but is anyone here experienced enough in matlab to help me with an error I'm having?

Error in ==> ode45 at 136
solver_name = 'ode45';

??? Output argument "varargout{4}" (and maybe others) not assigned during call to
"c:\program files\matlab\r2010a\toolbox\matlab\funfun\ode45.m>ode45".

Error in ==> pendulum at 8
[x1,z1,x2,z2] = ode45('pendfunc', [0 t], [theta1; 0; theta2; 0]);

I don't know what Output argument "varargout{4}" not assigned during call means. There's only 3 input arguments, and the 4 that were called should be properly defined.

Last edited by Bevo (2011-04-30 18:16:59)

2011-04-30 18:16:22

#599

FatherTed: xD; +3,936|6524|so randum

is that like pokemon? im good at pokemon

Small hourglass island
Always raining and foggy
Use an umbrella

2011-04-30 18:17:33

#600

Bevo: Nah; +718|6545|Austin, Texas

FatherTed wrote:
is that like pokemon? im good at pokemon

almost m8 except instead of pikachu and charizard you shove your head in an oven

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Hurricane2k9 wrote:

FatherTed wrote:

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