How exactly do logarithms work?

In summary: You will not be able to fully comprehend these formulas without studying Calculus. In summary, logarithms can be computed using different methods such as Taylor's series, but these methods require a deeper understanding of Calculus. Before logarithms were discovered, people used methods such as Borchardt's Algorithm to solve problems involving logarithms without using the log function, but these methods were slower and more tedious. The calculator calculates logs using a combination of more elementary processes, such as Borchardt's Algorithm, to compute logarithms.
  • #1
TidusBlade
18
0
I was just wondering what's the "magic" behind logarithms. Just took them in school, and I get the part that they're just the reverse of exponents but it still feels sort of like a mystery every time I solve a logarithm using a calculator. Just like how addition is the slow way of multiplication: [tex]6\times3 = 6 + 6 + 6[/tex] and multiplication is the slow way of raising something to some power: [tex]$ 6^3 = 6\times6\times6[/tex] so surely there must some long/slow way to do logarithms that was in use before they were discovered/invented? [tex]$ (\log _{2}^{32} = 5) = ?$[/tex]

Hopefully someone can shed some light on this, it's sort of bugging me that I have no idea what goes on behind the scenes, Thanks ^^
 
Last edited:
Mathematics news on Phys.org
  • #2
The more reliable characterization is Logarithms are exponents. Logarithms are not reverses of exponents; logarithmic functions are the inverses of exponential functions.

One first learns the rules of exponents with a common base. Derivations and exercises help to fix these rules. Later, when one studies functions, one reaches exponential functions, does some exercises, and then examines the idea of the inverse of an exponential function. Finally, one is shown the rules of logarithms, which are the same as the rules of exponents because logarithms ARE exponents. The notation appears different for logarithms than for exponents. Because this has a different appearance, students struggle with initial confusion.

Learn how to transcribe between exponential forms and logarithmic forms of equations; doing so is often very helpful:

b^x = y <------> LOG_b (y) = x [the logarithm base b of y equals x]

y = b^x is the inverse of y = LOG_b (x)
 
  • #3
Thanks for the reply but I think I might have worded my question wrongly... I know how to use logs and I know they're the inverse of exponential functions but was wondering how exactly would one go about computing logarithms without using the log function. Like if I wanted to figure out x in [tex]$ 4^x = 1024 $[/tex] without using logs and without guessing how would I do it? I guess I'm trying to find out how people solved that for x before logarithms were discovered.

The only thing close to what I was looking for is Borchardt's Algorithm: [tex]$ ln(x) \approx \frac{6\times(x - 1)}{x + 1 + 4x^{0.5}}[/tex]
I was looking for something like that, something that allows us to solve problems that include something raised to x without logs.

Thanks again symbolipoint but wasn't what I was looking for :)

//EDIT: What I meant by "I have no idea what goes on behind the scenes" is that I have no idea how the calculator calculates logs, surely it doesn't guess and it doesn't have a list of values ready, it must have computed my log by using a combination of more elementary processes, and that's sort of what I want to know.
 
Last edited:
  • #4
You could, for example, use the Taylor's series:
[tex]log(1+x)= \sum_{n= 1}^\infty \frac{x^n}{n}= x+ \frac{x^2}{2}+ \frac{x^3}{3}+ \cdot\cdot\cdot[/tex]
 
  • #5
You could, for example, use the Taylor's series:
[tex]log(1+ x)= \sum_{n=1}^\infty \frac{(-1)^{n+1}x^n}{n}= x- \frac{x^2}{2}+ \frac{x^3}{3}- \frac{x^4}{4}+ \cdot\cdot\cdot[/tex]
 
  • #6
TidusBlade said:
Thanks for the reply but I think I might have worded my question wrongly... I know how to use logs and I know they're the inverse of exponential functions but was wondering how exactly would one go about computing logarithms without using the log function. Like if I wanted to figure out x in [tex]$ 4^x = 1024 $[/tex] without using logs and without guessing how would I do it? I guess I'm trying to find out how people solved that for x before logarithms were discovered.

The only thing close to what I was looking for is Borchardt's Algorithm: [tex]$ ln(x) \approx \frac{6\times(x - 1)}{x + 1 + 4x^{0.5}}[/tex]
I was looking for something like that, something that allows us to solve problems that include something raised to x without logs.

Thanks again symbolipoint but wasn't what I was looking for :)

//EDIT: What I meant by "I have no idea what goes on behind the scenes" is that I have no idea how the calculator calculates logs, surely it doesn't guess and it doesn't have a list of values ready, it must have computed my log by using a combination of more elementary processes, and that's sort of what I want to know.

HallsofIvy has given examples of Taylor Series formulas, which are developed in the study of Calculus, usually the Second Semester course of College Calculus. Look at this as a way of being motivated to keep studying Math courses at least through Calculus 2.
 

Related to How exactly do logarithms work?

1. What is the definition of a logarithm?

A logarithm is the inverse operation of exponentiation. It is a mathematical function that represents the number of times a certain base number must be multiplied by itself to equal a given number.

2. How do logarithms solve exponential equations?

Logarithms can be used to solve exponential equations by isolating the variable in the exponent and using the logarithmic property that states logb(xn) = n*logb(x).

3. What is the relationship between logarithms and exponents?

The logarithm of a number is the exponent to which a base number must be raised to equal that number. For example, log2(8) = 3 because 23 = 8.

4. How do logarithms handle large numbers?

Logarithms are useful for handling large numbers because they condense them into smaller, more manageable values. This makes it easier to perform calculations and compare numbers that differ by several orders of magnitude.

5. What are some real-world applications of logarithms?

Logarithms are used in a variety of fields, including science, engineering, finance, and statistics. Some examples of real-world applications include earthquake intensity measurements, measuring the loudness of sound, and calculating pH levels in chemistry.

Similar threads

Replies
4
Views
2K
  • General Math
Replies
15
Views
3K
Replies
3
Views
1K
Replies
2
Views
1K
Replies
5
Views
3K
Replies
16
Views
1K
Replies
13
Views
2K
  • Precalculus Mathematics Homework Help
Replies
1
Views
920
  • Precalculus Mathematics Homework Help
Replies
1
Views
1K
  • General Discussion
Replies
1
Views
992
Back
Top