Math assistance please....

[Scarpozzi]

I'm trying to help one of my friends finish his CPSC homework. I'm terrible at math, so I need some help so we can go drink.

If you have a problem like 2^n = 8 n^4, how do you solve for n?

Do you do something with logs? I can't remember cause I haven't taken a math course in like 4 years. Thanks.

-Scar

 

[raptor13]

Press F2, then enter, and type "2^n=8*n^4,n)". Then hit enter again.

 

[melly]

Originally posted by: raptor13
Press F2, then enter, and type "2^n=8*n^4,n)". Then hit enter again.

:evil:

 

[Scarpozzi]

Originally posted by: raptor13
Press F2, then enter, and type "2^n=8*n^4,n)". Then hit enter again.

I meant to say, he's trying to do this the old fashioned way....with a pen and paper. 😉 We don't have Maple or any fun proggies to make this easier. Math sux. 😀

 

[Yax]

n = 0

 

[MRupe]

natural logs

 

[Dissipate]

Originally posted by: cheapbidder01
n = 0

Wrong. Zero doesn't work.

 

[Chumpman]

Originally posted by: raptor13
Press F2, then enter, and type "2^n=8*n^4,n)". Then hit enter again.

89 > you

 

[MRupe]

20.402 or.668

 

[dighn]

not sure if you can solve that analytically...

 

[MRupe]

Originally posted by: Chumpman

Originally posted by: raptor13
Press F2, then enter, and type "2^n=8*n^4,n)". Then hit enter again.

89 > you

it depends on if its 8*n^4 or (8*n)^4

 

[MRupe]

and how did you get 89
i get 32 the other way

 

[BigPoppa]

89 won't solve that directly, I tried.

 

[Dissipate]

Originally posted by: BigPoppa
89 won't solve that directly, I tried.

Some equations can't be solved, only approximated.

 

[eLiu]

I believe this is what they call a "transcendental function." Not all of these types of functions can be solved analytically--I don't think this one can be.

You could use some sort of algorithm to approximate the roots though...for example, the Newton-Raphson method or fixed point iterations.

-Eric

 

[upsciLLion]

I got x = -.5413599318, x = .66751844707

I graphed y1 = 2^n and y2 = 8n^4 and evaluated the intersection points. Hopefully that helps! 😛

ups

 

[Zorba]

n = -0.5413599318 🙂

 

[VTboy]

How come when I post a math question hardly anyone comes to help me. look all of these people helping him.

 

[Zorba]

What is your question?

 

[Dissipate]

Originally posted by: VTboy
How come when I post a math question hardly anyone comes to help me. look all of these people helping him.

Uh, cause you post math questions in diffierential equations. This is a lot farther down the trough. Also, differential equations take a lot more time and attention, even for someone who has mastered them and people are too lazy.

 

[VTboy]

Zorba this is a link to my question.

http://forums.anandtech.com/messageview.cfm?catid=38&threadid=1252379

 

[Joker81]

2^n = 8 n^4

well 8= 2^3
so you divide both sides by 2^3

You get 2^n-3 = n^4

(n Log 2 - 3log(2) = 4 * log (n)

n log 2 - 4 log n = 3 log 2

divide by log2

get n - 4*log(n)/log(2) = 3
take e^ to both sides

get

(e^x)*x^(-4/ln(2))=e^3


which roughly equals

2.71828^x*(x^-5.77078)=20.0855


you could put one of the x's on the other side and get



x^-5.77078 = e^(3-x)


now solve haha