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Math question.  pow(a,b)

Posted on 2000-05-11
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Last Modified: 2010-04-01
What is the easiest way to use java.lang.Math to solve the equation 10^x = 3000? Solve for x.
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Question by:kevinhol
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Expert Comment

by:tgoetze
ID: 2802811
To solve for x, you take the log of both sides. Here log means the log base 10. This results in a solution of:
x = log(3000);

This is done via the log() method in java.lang.Math.

double x = java.lang.Math.log(3000.0);
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Author Comment

by:kevinhol
ID: 2804871
Adjusted points from 50 to 100
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Author Comment

by:kevinhol
ID: 2804872
Thanks tqoetze,

Although you did answer my original question, I have decided to change it to include different bases other than 10. ie 4^x = 3000. I've up'd the points and will hold them for you if you can answer.
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LVL 3

Expert Comment

by:tgoetze
ID: 2804944
Good thing you ask for some more details, I checked and found out that java.lang.Math.log is the natural logarithm, which is the log base e.

For convseion, the general rule is that the log base a of x is equal to the log base c of x divided by the log base c of a. This allows the conversion between bases.

To answer your original question (which I was wrong with first), you would need to do:

double x = java.lang.Math(3000.0)/java.lang.Math(10.0);

And for your next problem:

To solve 4^x = 3000. You simply do
log(3000)/log(4).
In java:

double x = java.lang.Math.log(3000.0)/java.lang.Math.log(4.0);

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Accepted Solution

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tgoetze earned 400 total points
ID: 2807853
kevinhol,

Does the answer I posted make sense? Does it answer your question for you? Please let me know if you have any further questions about this.

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Author Comment

by:kevinhol
ID: 2811046
Thanks, it worked well in my program.

P.S. I thought I excepted your comment as an answer last week, sorry for the delay.
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