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Math Geeks, Halp!

...or anyone with average discrete math skills.

Gotta find a solution to the following recurrence relation:

a_n = 2na_n-1, a₀ = 3

a₁ = 2(1)(3) = 6
a₂ = 2(2)(6) = 24
a₃ = 2(3)(24) = 144
a₄ = 2(4)(144) = 1152

a_n = ???

This is driving me crazy!!!

Hmm.

Well 6*4= 24. 24*6=144. 144*8=1152. Does that point you in the right direction?

42.

quote:

Originally posted by Halcyon+On+On 42.

quote:

Originally posted by Ted Promo quote: Originally posted by Halcyon+On+On 42.

Stu, stop using your magical heathen quoting skills!

i thought i was good at math, but i think i had too much wine to be able to read that one.

Now what's the question?

quote:

Originally posted by WittyHandle Now what's the question?

Find a solution (formula) that will find you any term (n) you plug in.

Basically you find another way to express the first formula given but without using a_n-1. It eliminates the need need to know the first term in the sequence, 3.

your solution is: 6n * (n-1)! * 2^(n-1)

note that 0! = 1

btw, how the hell do you do subscript/superscript on this forum?

Re: Re: Math Geeks, Halp!

quote:

Originally posted by Meat187 an = 3*2n*(n-1)!

HA! you're too late

edit: damnit, i just realized a problem in my solution

edit2: why did you delete your post, it was right...

No, it wasn't.

Correct is: a_n = 3*2ⁿ*n!

The problem was that (-1)! is not defined.

quote:

Originally posted by Meat187 No, it wasn't. Correct is: an = 3*2n*n! The problem was that (-1)! is not defined.

oh ok. I guess if you mutate mine a little bit it was right all along.

and how the hell do you add superscript..

quote:

Originally posted by Pokit and how the hell do you add superscript..

If you can quote superscript you can write superscript.
Just look at the tags used there.

quote:

Originally posted by Meat187 If you can quote superscript you can write superscrip.

yeah i just noticed. lol.

What was just messing with my mind is that my equation can be turned into your equation with a few operations:
6n*(n-1)!*2^n-1 = 6 * (n*(n-1)!) * 2ⁿ/2 = 3*n!*2ⁿ

But my equation won't work with n=0 where yours does.

Im just dumb when it comes to math lol

Finally, you guys are fucking geniuses. What math background do you guys have? I know this is fairly easy stuff, probably equivalent to alg 2, but this one in particular was really mind-fucking me.

And since you helped me, subscript is "sub" with HTML tags, or "sup" for superscript.

Thanks fellas.

decent thread. I finished my mech. eng degree recently so I have seen my fair share of math.

Question for the math geeks out there. I saw this my on a final I took and have never worked on this before? "3/2!" a factorial of a fraction. I did my research after the exam and it has to do with the gamma function, etc and know what it equals?

http://en.wikipedia.org/wiki/Factorial <--non integer values

My main concern is what class would you learn this in even though we did the typical factorial in HS?

f(x) = mx + b

quote:

Originally posted by Comrade Stalin f(x) = mx + b

Why did the chicken cross the M�bius strip?

To get to the same side

....

"http://www.tfproject.org/tfp/tilted-humor/163-math-jokes-warning-super-lame.html"

I've a Calc II Final tomorrow morning. If I don't pass it, I fail the course. First time I've ever significantly struggled with mathematics. Damn you v dus and (n+1)s.

quote:

Originally posted by Sykonee I've a Calc II Final tomorrow morning. If I don't pass it, I fail the course. First time I've ever significantly struggled with mathematics. Damn you v dus and (n+1)s.

I remember finding areas and volume of rings. Not the hardest but having a decent professor helps.

quick review below
http://tutorial.math.lamar.edu/Clas...cII/CalcII.aspx

good luck

quote:

Originally posted by Trancealot I remember finding areas and volume of rings. Not the hardest but having a decent professor helps.

I've done fine with the homework and stuff, it's the exams that keep tripping me up, and it doesn't help that they're worth such a significant portion of the final grade.

Nor does the fact I'm in a class with a bunch of summer Asian students, putting me significantly under the curve of a class for the first time since Grade 8 woodshop.

quote:

Originally posted by IpLaYWiTLiGhTs Finally, you guys are fucking geniuses. What math background do you guys have? I know this is fairly easy stuff, probably equivalent to alg 2, but this one in particular was really mind-fucking me. And since you helped me, subscript is "sub" with HTML tags, or "sup" for superscript. Thanks fellas.

You're welcome

I actually don't have that much of a background in math. I've taken 3 calc courses and an Ordinary Differential Equations + Linear algebra course (Partial differential equations next semester...)

Anyway, my approach to solve the problem, ironically, had nothing to do with any kind of formal mathematical algorithm/formula. All I did was take a look at any patterns I could see. I saw that each level was divisible by 3n, and that each level was divisible by (n-1)!, so i pulled that out and saw that the sequence just followed 2^n-1, so put all of it together and do a little bit of manipulation adn you get 3*n!*2ⁿ

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