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Geek Culture / Simple math question

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Jeku
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Posted: 2nd Feb 2005 04:39
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I've totally forgotten how to do this, and if someone could help me out I'd be much obliged.

20 = 3log2(1 + X)

How can I solve for X? The 2 is small, by the way.

Thanks


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Osiris
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Posted: 2nd Feb 2005 05:29
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use a graphing calculator, lol, hey whats this for

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Jeku
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Posted: 2nd Feb 2005 05:29 Edited at: 2nd Feb 2005 05:30
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This is for my assignment, and I don't have a calculator And I have to show my work, so no, I can't just use PHP to solve it.

There has to be a way to flip the equation around--- something to do with exponents, but I completely forgot.


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Osiris
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Posted: 2nd Feb 2005 05:31
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oh have fun... lol, i have no idea what that is

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TravisP
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Posted: 2nd Feb 2005 05:32
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18=3log2x
Is some of it I think.

Note: The above I didn't say, your just crazy.

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Luke B
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Posted: 2nd Feb 2005 06:01
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X is 86.856210703539267105289682438964

Working:

First of all I do 3log
Then I square that
Then I divide 20 by that answer
Then take 1 off that answer because that answer is X + 1 and you want X

Just round your answer and enjoy

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TKF15H
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Posted: 2nd Feb 2005 06:05 Edited at: 2nd Feb 2005 06:45
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20 = 3log2(1 + X)

gonna flip it around just because...

3log2(1 + X) = 20

log2( (1 + X)^3 ) = 20

2^20 = (1 + X)^3

1048576 = (1 + X)^3

find the cubic root of 1048576 to the power of 3:

101.59366^3 = (1 + X)^3

cut out the ^3 on both ends:

101.59366 = 1 + X

X = 100.59366

[edit] fixed a silly mistake. So much for being awake

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Neofish
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Posted: 2nd Feb 2005 06:07 Edited at: 2nd Feb 2005 06:09
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EDIT: TKs answer makes no sense to me

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Luke B
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Posted: 2nd Feb 2005 06:07
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damn TKF15H, your awake

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Rob K
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Posted: 2nd Feb 2005 06:25 Edited at: 2nd Feb 2005 06:36
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I make it slightly different:

20 = 3log2(1+x) -> divide by 3

(20/3) = log2(1+x) -> 2 raised to (20/3) = (1+x), so lets rearrange

(1+x) = 2^(20/3) -> Solve 2^(20/3)

(1+x) = 101... -> Subtract 1 to get x

x = 100.59

You can check it with Excel if you wish

Quote: "
log2( (1 + X)^3 ) = 20

2^20 = 3.(1 + X)
"


You can't do that! - I think you mean 2^20=(1+x)^3


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TKF15H
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Posted: 2nd Feb 2005 06:42
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That's right, Rob. I noticed the mistake and you posted while I was editing.

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Peter H
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Posted: 2nd Feb 2005 09:27
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do you mean the log of 2*(1+x) or a log with a base of 2???

if it's a base of 10 (default) then x=2.32079e6

or 500000*(10^2/3)-1

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Jeku
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Posted: 2nd Feb 2005 19:25
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Thank you all for your help--- much obliged I suck at math and I don't want to ever mess with it again.


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Rob K
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Posted: 2nd Feb 2005 22:19
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Quote: " do you mean the log of 2*(1+x) or a log with a base of 2???"


He means log to the base 2. Also written as:

(log to the base 10 of X)
-------------------------
(log to the base 10 of 2)


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Coding Fodder
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Posted: 3rd Feb 2005 00:14
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Shucks, I always get to the math questions to late. Good work Rob K.

Quote: "I suck at math and I don't want to ever mess with it again.
"


As a mathematician I cringe when people say that. Especially if they are into a hobby like programming. Learn to like it, Math is your friend. Besides being just so beautiful. *sob*

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David T
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Posted: 3rd Feb 2005 00:40
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Only on a programming forum does this sort of question get described as "simple"

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Coding Fodder
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Posted: 3rd Feb 2005 00:44
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umm it is

Something really catchy that makes people stop and think about the meaning of life and say to themselves "My but thats clever"
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Rob K
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Posted: 3rd Feb 2005 01:30
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Agreed. Years ago it would have been 3rd form (ie. for 13yr olds) maths. Now it doesn't feature in the syllabus until 6th form (16-18yr olds).


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Peter H
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Posted: 3rd Feb 2005 03:53
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Quote: "Agreed. Years ago it would have been 3rd form (ie. for 13yr olds) maths. Now it doesn't feature in the syllabus until 6th form (16-18yr olds).
"

yeah it seems they are teaching stuff waaayy too slowly in 1st-8th grades..then go an ok speed in high school...then speed up like crazy for colledge

i skipped 4th, 5th and 7th grade math lol...i was so annoyed with doing the same stuff over and over again (i could multiply at age 5)...I.E. Addition, Subtraction and Multiplication...that's all you do in 1st-5th grades it seems...

Quote: " Math is your friend. Besides being just so beautiful. *sob*"

amen (yeah i'm a math nerd also...15 and taking...well...calculus at teh colledge )

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Jeku
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Posted: 3rd Feb 2005 06:47
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Well we learned this stuff in the later grades, but truly I don't enjoy it one bit. However since I'm graduating with my computer science degree in April, you should know that I've taken my fair share of difficult math courses


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