Laws of Logarithms

4.3 Laws of Logarithms
 
The image is a visual representation of logarithms. It consists of three main sections. 1. The left section contains a text box with the definition of a logarithm: ‘A logarithm is the power to which a number (the base) must be raised to produce a given number.’ 2. The middle section has a title that reads ‘LAWS OF LOGARITHMS.’ 3. The right section shows a mathematical expression: ‘IF b^y = x, then log_b(x) = y.’ Arrows connect the three sections, indicating a flow of information from the definition to the laws and then to the mathematical expression. The image has a clean and educational design.
 
Basic Laws of Logarithms
Product Law

\(\log_b{(xy)}=\log_b{(x)}+\log_b{(y)}\)

Quotient Law

\(\log_b{\left( \dfrac{x}{y} \right)}=\log_b{(x)}-\log_b{(y)}\)

Power Law

\(\log_b{(x^n)}=n\log_b{(x)}\)

Change of Base Formula

\(\log_b{(x})=\dfrac{\log_k{(x)}}{\log_k{(b)}}\) (for any base \(k\))

 
Special Logarithms
  • Common Logarithm: Base \(10\), denoted as \(\log{(x)}\).
  • Natural Logarithm: Base \(e\) (Euler's number, approximately \(2.718\)), denoted as \(\ln{(x)}\).
 
Solving Logarithmic Equations
  • Converting to Exponential Form: Use the definition \(\log_b{x}=y \Rightarrow b^y=x\).
  • Applying Logarithm Laws: Simplify and solve equations using the product, quotient, and power laws.
  • Example:
    \(\begin{aligned} \log_2{(x)}+\log_2{(x-1)}&=3 \\ \log_2{(x(x-1))}&=3 \\ x(x-1)&=8 \end{aligned}\)
 
Properties of Logarithms
Logarithm of \(1\)

\(\log_b{(1)}=0\) (since \(b^0=1\))

Logarithm of the Base

\(\log_b{(b)}=1\) (since \(b^1=b\))

 
Graph of Logarithmic Functions
Example

A graph displaying logarithmic and exponential functions, along with the line y=x.

Description
  • Shape: The graph of \(y=\log_a(x)\) is a curve that increases slowly and passes through the point \((1,0)\).
  • Asymptote: The vertical line \(x=0\) is an asymptote.
  • Domain and Range: The domain are \(x>0\), while the range are all real numbers.
  • Relation with Exponential Function: The exponential and logarithmic functions are reflection of one another in the straight line \(y=x\). The exponential and logarithmic functions are inverse functions of one another.
 

 

Laws of Logarithms

4.3 Laws of Logarithms
 
The image is a visual representation of logarithms. It consists of three main sections. 1. The left section contains a text box with the definition of a logarithm: ‘A logarithm is the power to which a number (the base) must be raised to produce a given number.’ 2. The middle section has a title that reads ‘LAWS OF LOGARITHMS.’ 3. The right section shows a mathematical expression: ‘IF b^y = x, then log_b(x) = y.’ Arrows connect the three sections, indicating a flow of information from the definition to the laws and then to the mathematical expression. The image has a clean and educational design.
 
Basic Laws of Logarithms
Product Law

\(\log_b{(xy)}=\log_b{(x)}+\log_b{(y)}\)

Quotient Law

\(\log_b{\left( \dfrac{x}{y} \right)}=\log_b{(x)}-\log_b{(y)}\)

Power Law

\(\log_b{(x^n)}=n\log_b{(x)}\)

Change of Base Formula

\(\log_b{(x})=\dfrac{\log_k{(x)}}{\log_k{(b)}}\) (for any base \(k\))

 
Special Logarithms
  • Common Logarithm: Base \(10\), denoted as \(\log{(x)}\).
  • Natural Logarithm: Base \(e\) (Euler's number, approximately \(2.718\)), denoted as \(\ln{(x)}\).
 
Solving Logarithmic Equations
  • Converting to Exponential Form: Use the definition \(\log_b{x}=y \Rightarrow b^y=x\).
  • Applying Logarithm Laws: Simplify and solve equations using the product, quotient, and power laws.
  • Example:
    \(\begin{aligned} \log_2{(x)}+\log_2{(x-1)}&=3 \\ \log_2{(x(x-1))}&=3 \\ x(x-1)&=8 \end{aligned}\)
 
Properties of Logarithms
Logarithm of \(1\)

\(\log_b{(1)}=0\) (since \(b^0=1\))

Logarithm of the Base

\(\log_b{(b)}=1\) (since \(b^1=b\))

 
Graph of Logarithmic Functions
Example

A graph displaying logarithmic and exponential functions, along with the line y=x.

Description
  • Shape: The graph of \(y=\log_a(x)\) is a curve that increases slowly and passes through the point \((1,0)\).
  • Asymptote: The vertical line \(x=0\) is an asymptote.
  • Domain and Range: The domain are \(x>0\), while the range are all real numbers.
  • Relation with Exponential Function: The exponential and logarithmic functions are reflection of one another in the straight line \(y=x\). The exponential and logarithmic functions are inverse functions of one another.