A logarithm is a mathematical concept that represents the exponent to which a base must be raised to produce a given number. In simple terms, logarithms are the inverse operations of exponentiation. For example, since 10² = 100, then log₁₀ 100 = 2.
In this article we are going to learn about the history, types, formulas, and logarithm examples, and understand why they are so important in modern mathematics and science.
Table of Contents
The concept of logarithms was introduced in the 17th century by John Napier. They quickly became an essential tool in science and navigation, helping simplify complex calculations before the invention of calculators.
A logarithm tells us how many times a base is multiplied by itself to reach a given number.
The general form is:
log₍b₎ x = n ⇔ bⁿ = x
Where:
x is the argument (the number we want to reach)
b is the base (must be a positive real number ≠ 1)
n is the exponent or power
Example:
log₍3₎(27) = 3 → Since 3³ = 27
Common Logarithm (Base 10)
Notation: $log₁₀(x) or simply log(x)$
Example: log(1000) = 3 because 10³ = 1000
Natural Logarithm (Base e)
Notation: $ln(x) or logₑ(x)$
e ≈ 2.71828 (Euler’s number)
Example: ln(78) ≈ 4.357
Product Rule
$log₍b₎(mn) = log₍b₎m + log₍b₎n$
Quotient Rule
$log₍b₎(m/n) = log₍b₎m − log₍b₎n$
Power Rule
$log₍b₎(mⁿ) = n × log₍b₎m$
Change of Base Rule
$log₍b₎m = log₍a₎m / log₍a₎b$
Base Switch Rule
$log₍b₎a = 1 / log₍a₎b$
Derivative of log
If $f(x) = log₍b₎(x)$, then
f'(x) = 1 / (x × ln(b))
Integral of log
$∫log₍b₎(x) dx = x(log₍b₎x − 1/ln(b)) + C$
Other Properties
$log₍b₎(b) = 1$ $log₍b₎(1) = 0$
$log₍b₎(0) = undefined$
$log₍b₎(mn) = log₍b₎(m) + log₍b₎(n)$
$log₍b₎(m/n) = log₍b₎(m) − log₍b₎(n)$
$log₍b₎(xʸ) = y × log₍b₎(x)$
$log₍b₎(√n) = (1/2) × log₍b₎(n)$
$m log₍b₎(x) + n log₍b₎(y) = log₍b₎(xᵐyⁿ)$
Example 1:
log₂(64) = ?
→ 2⁶ = 64 → Answer: 6
Example 2:
log₁₀(100) = ?
→ 10² = 100 → Answer: 2
Example 3:
log₃x = log₃4 + log₃7
→ By product rule: log₃x = log₃(28)
→ x = 28
Example 4:
log₂x = 5
→ Convert to exponential: 2⁵ = x → x = 32
Example 5:
log₅(1/25) = log₅1 − log₅25 = 0 − 2 = –2
Evaluate: log₄(64)
Solve: log₂x = 3
Simplify: log₅(25) + log₅(4)
Find x: $log₃x = log₃9 + log₃3$
Differentiate:$ f(x) = logₑ(x² + 1) $
Logarithms are foundational tools in mathematics used for simplifying complex calculations. From representing large numbers efficiently to real-world applications in science and engineering, they are essential to understand and master. Start with the basic rules and properties and practice real-world logarithm examples to gain confidence.
Ans. Logarithms express the exponent needed for a base to reach a given number. For example, log₁₀(100) = 2.
Ans.Common logarithm (base 10) and natural logarithm (base e).
Ans.It is undefined. No exponent of a positive base ever equals zero.
Ans.log₁₀(10) = 1
Ans.
$\log_{b}(mn) = \log_{b} m + \log_{b} n$
$\log_b\left(\frac{m}{n}\right) = \log_b m - \log_b n$
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