Laws of Indices

4.1 Law of Indices
 
This image has a blue background and features a concept from mathematics titled ‘Law of Indices.’ The title is enclosed in a blue, irregularly shaped bubble. There are two additional bubbles connected to the title bubble with red arrows. 1. The top bubble contains the text: ‘Indices, or exponents, represent repeated multiplication of a number by itself.’ 2. The bottom bubble contains the text: ‘If a is a number and n is a positive integer, then a^n = a × a × ... × a (n times).’ In the bottom left corner, there is a logo with the text ‘Pandai.’
 
Basic Laws of Indices
  • Product Law: \(a^m\times a^n=a^{m+n}\)
  • Quotient Law: \(\dfrac{a^m}{a^n}=a^{m-n}\) (for \(a\neq 0\))
  • Power Law: \((a^m)^n=a^{mn}\)
  • Zero Exponent: \(a^0=1\) (for \(a\neq 0\))
  • Negative Exponent: \(a^{-n}=\dfrac{1}{a^n}\) (for \(a\neq 0\))
 
Fractional Indices
  • \(a^{\frac{1}{n}}\) represent the \(n\)-th root of \(a:a^{\frac{1}{n}}=\sqrt[n]{a}\)
  • \(a^\frac{m}{n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m\)
 
Simplifying Expressions
  • Combine same terms using the laws of indices.
  • Simplify expressions with indices by applying the appropriate laws.
 
Solving Problems Involving Indices
If \(a^m=a^n\), then \(m=n\) or if \(a^m=b^m\), then \(a=b\) when \(a \gt 0\) and \(a \neq 1\).
 
Important Concepts
  • Base: The number that is multiplied.
  • Exponent: The number of times the base is multiplied by itself.
  • Index Form: Expression written with exponent such as \(2^3\).
 
Example \(1\)
Question

Simplify the following algebraic expression.

\((5x^{-1})^3\times4xy^2 \div (xy)^{-4}\)

Solution

\(\begin{aligned} &(5x^{-1})^3\times4xy^2 \div (xy)^{-4} \\ &=\dfrac{(5x^{-1})^3\times4xy^2}{(xy)^{-4}} \\ &=5^3x^{-3}\times 4xy^2 \times (xy)^4 \\ &=125\times 4\times x^{-3+1+4}\times y^{2+4} \\ &=500x^2y^6. \end{aligned}\)

 
Example \(2\)
Question

Show that \(7^{2x-1}=\dfrac{49^x}{7}\).

Solution

Solve for the equation on the left hand side.

\(\begin{aligned} 7^{2x-1}&=\dfrac{7^{2x}}{7} \\ &=\dfrac{49^x}{7}. \end{aligned}\)

 
Example \(3\)
Question

Solve the following equation.

\(32^x=\dfrac{1}{8^{x-1}}\)

Solution

\(\begin{aligned} 32^x&=\dfrac{1}{8^{x-1}} \\ 2^{5x}&=2^{-3(x-1)} \\ 5x&=-3x+3 \\ 8x&=3 \\ x&=\dfrac{3}{8}. \end{aligned}\)

 

 Laws of Indices

4.1 Law of Indices
 
This image has a blue background and features a concept from mathematics titled ‘Law of Indices.’ The title is enclosed in a blue, irregularly shaped bubble. There are two additional bubbles connected to the title bubble with red arrows. 1. The top bubble contains the text: ‘Indices, or exponents, represent repeated multiplication of a number by itself.’ 2. The bottom bubble contains the text: ‘If a is a number and n is a positive integer, then a^n = a × a × ... × a (n times).’ In the bottom left corner, there is a logo with the text ‘Pandai.’
 
Basic Laws of Indices
  • Product Law: \(a^m\times a^n=a^{m+n}\)
  • Quotient Law: \(\dfrac{a^m}{a^n}=a^{m-n}\) (for \(a\neq 0\))
  • Power Law: \((a^m)^n=a^{mn}\)
  • Zero Exponent: \(a^0=1\) (for \(a\neq 0\))
  • Negative Exponent: \(a^{-n}=\dfrac{1}{a^n}\) (for \(a\neq 0\))
 
Fractional Indices
  • \(a^{\frac{1}{n}}\) represent the \(n\)-th root of \(a:a^{\frac{1}{n}}=\sqrt[n]{a}\)
  • \(a^\frac{m}{n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m\)
 
Simplifying Expressions
  • Combine same terms using the laws of indices.
  • Simplify expressions with indices by applying the appropriate laws.
 
Solving Problems Involving Indices
If \(a^m=a^n\), then \(m=n\) or if \(a^m=b^m\), then \(a=b\) when \(a \gt 0\) and \(a \neq 1\).
 
Important Concepts
  • Base: The number that is multiplied.
  • Exponent: The number of times the base is multiplied by itself.
  • Index Form: Expression written with exponent such as \(2^3\).
 
Example \(1\)
Question

Simplify the following algebraic expression.

\((5x^{-1})^3\times4xy^2 \div (xy)^{-4}\)

Solution

\(\begin{aligned} &(5x^{-1})^3\times4xy^2 \div (xy)^{-4} \\ &=\dfrac{(5x^{-1})^3\times4xy^2}{(xy)^{-4}} \\ &=5^3x^{-3}\times 4xy^2 \times (xy)^4 \\ &=125\times 4\times x^{-3+1+4}\times y^{2+4} \\ &=500x^2y^6. \end{aligned}\)

 
Example \(2\)
Question

Show that \(7^{2x-1}=\dfrac{49^x}{7}\).

Solution

Solve for the equation on the left hand side.

\(\begin{aligned} 7^{2x-1}&=\dfrac{7^{2x}}{7} \\ &=\dfrac{49^x}{7}. \end{aligned}\)

 
Example \(3\)
Question

Solve the following equation.

\(32^x=\dfrac{1}{8^{x-1}}\)

Solution

\(\begin{aligned} 32^x&=\dfrac{1}{8^{x-1}} \\ 2^{5x}&=2^{-3(x-1)} \\ 5x&=-3x+3 \\ 8x&=3 \\ x&=\dfrac{3}{8}. \end{aligned}\)