Laws Of Indices Mathematics Pdf
Laws of Indices
Here we will learn everything you need to know about the laws of indices for GCSE & iGCSE maths (Edexcel, AQA and OCR). You'll learn what the laws of indices are and how we can use them. You'll learn how to multiply indices, divide indices, use brackets and indices, how to raise values to the power of 0 and to the power of 1, as well as fractional and negative indices.
Look out for the laws of indices worksheets and exam questions at the end.
What are indices?
An index is a small number that tells us how many times a term has been multiplied by itself.
The plural of index is indices.
Below is an example of a term written in index form:
\[4^{3}\]
4 is the base and 3 is the index.
We can read this as '4 to the power 3'
Another way of expressing 43 is
\[4 \times 4 \times 4=64\]
Indices can be positive or negative numbers.
Index Form
\[ 2^{3} \]
\[2^{2}\]
\[2^{1}\]
\[2^{0}\]
\[2^{-1}\]
\[2^{-2}\]
\[2^{-3}\]
Expanded Form
\[2 \times2 \times 2\]
\[2\times 2\]
\[2\]
\[1\]
\[\frac{1}{2}\]
\[\frac{1}{2^{2}}=\frac{1}{2} \times \frac{1}{2}\]
\[\frac{1}{2^{3}}=\frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}\]
Value
\[8\]
\[4\]
\[2\]
\[1\]
\[\frac{1}{2}=0.5\]
\[\frac{1}{4}=0.25\]
\[\frac{1}{8}=0.125\]
Moving up the rows we get 2 times larger per row.
Moving down the rows we get 2 times smaller per row.
What are the laws of indices?
Laws of indices provide us with rules for simplifying calculations or expressions involving powers of the same base. This means that the larger number or letter must be the same.
E.g.
\[2^{5} \times 2^{3}=2^{8}\]
\[x^{10} \div x^{4}=10^{6}\]
We cannot use laws of indices to evaluate calculations when the bases are different
E.g.
\[2^{5} \times 3^{3}\]
\[x^{10} \div y^{4}\]
We can however evaluate these calculations. Check out our other pages to find out how.
Laws of indices methods
There are several laws of indices (sometimes called indices rules), including multiplying, dividing, power of 0, brackets, negative and fractional powers.
For examples and practice questions on each of the rules of indices, as well as how to evaluate calculations with indices with different bases, follow the links below.
See also: Index notation
1. Multiplying indices
When multiplying indices with the same base, add the powers.
\[a^{m} \times a^{n}=a^{m+n}\]
Step by step guide: Multiplying indices
2. Dividing indices
When dividing indices with the same base, subtract the powers.
\[a^{m} \div a^{n}=a^{m-n}\]
Step by step guide: Dividing indices
3. Brackets with indices
When there is a power outside the bracket multiply the powers.
\[(a^{m})^{n}=a^{m \times n}\]
Step by step guide: Brackets with indices
4. Power of 0
Anything raised to the power of 0 is equal to 1.
\[a^{0}=1\]
Step by step guide: Power of 0
5. Negative indices
When the index is negative, put it over 1 and flip (write its reciprocal) to make it positive.
\[a^{-m}=\frac{1}{a^{m}}\]
Step by step guide: Negative indices
6. Fractional indices (H)
When the index is a fraction, the denominator is the root of the number or letter, then raise the answer to the power of the numerator.
\[x^{\frac{a}{b}}=(\sqrt[b]{x})^{a}\]
Step by step guide: Fractional indices
Laws of indices worksheets
Get your free laws of indices worksheet of 20+ questions and answers. Includes reasoning and applied questions.
DOWNLOAD FREE
Laws of indices worksheets
Get your free laws of indices worksheet of 20+ questions and answers. Includes reasoning and applied questions.
DOWNLOAD FREE
How to use the laws of indices
We can use the laws of indices to simplify expressions.
Law 1: multiplying indices
When multiplying indices with the same base, add the powers.
\[a^{m} \times a^{n}=a^{m+n}\]
1 Add the powers.
2 Multiply any coefficients.
…………………………………………………………………………………………………………………………………………………….
Example
Simplify
\[4 a^{3} \times 7 a^{2}\]
This can be written as
\[4 a^{3} \times 7 a^{2}=4 \times a \times a \times a \times 7 \times a \times a\]
1 Add together the indices 3 and the 2.
\[3 + 2 = 5\]
2 Multiply 4 and 7 together.
\[4 \times 7 =28\]
So,
\[4 a^{3} \times 7 a^{2}=28 a^{5}\]
Law 2: dividing indices
When dividing indices with the same base, subtract the powers.
\[a^{m} \div a^{n}=a^{m-n}\]
- Subtract the indices.
- Divide any coefficients of the base number or letter.
…………………………………………………………………………………………………………………….………………………………
Example
Simplify
\[21 a^{9} \div 7 a^{2}\]
Subtract the indices 9 and 2.
Divide the coefficients 21 and 7.
\[21 ÷ 7 = 3\]
So,
\[21 a^{9} \div 7 a^{2}=3a^{7}\]
Law 3: brackets with indices
When there is a power outside the bracket multiply the powers.
\[(a^{m})^{n}=a^{m \times n}\]
- Multiply the indices.
- Raise all coefficients inside the bracket to the power outside the bracket.
Why does this work?
Let's look at
\[(a^{3})^{4}\]
This algebraic expression has been raised to the power of 4, which means:
\[a^{3} \times a^{3} \times a^{3} \times a^{3}\]
We know when we multiply indices with the same base, we must add the powers.
\[a^{3} \times a^{3} \times a^{3} \times a^{3}=a^{12}\]
Is there a quicker way to work this out?
Simplifying
\[(a^{3})^{4}=a^{3 \times 4}=a^{12}\]
When we have brackets and indices we can multiply the powers.
Brackets with indices examples
Example 1: no coefficient in front of base
Simplify and leave your answer in index form.
\[(a^{3})^{4}\]
Multiply the powers 3 and the 4.
\[3\times 4=12\]
So,
\[\left(a^{3}\right)^{4}=a^{12}\]
Example 2: coefficient inside bracket
Simplify and leave your answer in index form.
\[(10 a^{3})^{2}\]
Multiply the indices 3 and the 2.
Raise 10 to the power of 2.
\[10^{2}=100\]
So,
\[\left(10 a^{3}\right)^{2}=100 a^{6}\]
Example 3: negative indices
Simplify and leave your answer in index form.
\[(-4a^{-3})^{2}\]
Multiply the indices -3 and the 2.
Raise -4 to the power of 2.
\[(-4)^{2}=16\]
So,
\[\left(-4 a^{-3}\right)^{2}=16 a^{-6}\]
Law 4: power of 0
Anything raised to the power of 0 is equal to 1.
Example
Simplify
\[12a^{0}\]
\[= 12 (1) = 12\]
We can see that
Multiplying anything by 1 leaves it unchanged, this is called the multiplicative identity.
So,
\[12 a^{0}=12\]
Law 5: negative indices
When the index is negative, put it over 1 and flip to make it positive.
\[a^{-m}=\frac{1}{a^{m}}\]
- Put the term over 1.
- Flip the fraction to make the index positive.
- Simplify if necessary.
Example
Simplify
\[(2a)^{-3}\]
Notice how the index affects the entire bracket
Flip and change the power -3 to +3.
Simplify the denominator.
\[=\frac{1}{8a^{3}}\]
So,
\[(2 a)^{-3}=\frac{1}{8 a^{3}}\]
Law 6: fractional indices (H)
When the index is a fraction, the denominator is the root of the number or letter, then raise the answer to the power of the numerator.
\[x^{\frac{a}{b}}=(\sqrt[b]{x})^{a}\]
- Use the denominator to find the root of the term
- Raise the answer to the power of the numerator
Example
Evaluate
\[27^{\frac{2}{3}}\]
Use the denominator to find the cube root of the number or letter.
Raise the answer to the power of the numerator.
\[3^{2}=9\]
So,
\[27^{\frac{2}{3}}=9\]
Common misconceptions
- The multiplication and division laws can only be used for terms with the same base
You cannot simplify
\[a^{4} \times b^{3}\]
as the bases are different
- When a power is outside the bracket you must raise all terms inside the bracket by that power
E.g.
When we simplify
\[(4a)^{2}\]
We must remember to square both the 4 and the a. It is common to forget to square the 4.
\[(4 a)^{2}=4 a \times 4 a=4^{2} a^{2}=16 a^{2}\]
The brackets mean the entire term is squared.
- Confusing integer and fractional powers
Raising a term to the power of 2 means we square it
E.g.
\[a^{2}=a \times a\]
Raising a term to the power of ½ means we find the square root of it
E.g.
\[a^{\frac{1}{2}}=\pm \sqrt{a}\]
Raising a term to the power of 3 means we cube it
E.g.
\[a^{3}=a \times a \times a\]
Raising a term to the power of ⅓ means we find the cube root of it
E.g.
\[a^{\frac{1}{3}}=\sqrt[3]{a}\]
- Confusing positive and negative powers
We can have decimal, fractional, negative or positive integers.
- Indices, powers or exponents
Indices can also be called powers or exponents.
Practice laws of indices questions
We need to multiply the coefficients
4\times5=20
Since the base number is the same in each term, we can add the indices
6+(-2)=4
This means
4 a^{6} \times 5 a^{-2}=20 a^{4}
We need to multiply the coefficients
-3\times6=-18
Since the base number is the same in each term, we can add the indices
4b+7b=11b
This means
-3 a^{4 b} \times 6 a^{7 b}=-18 a^{11 b}
We need to multiply the coefficients
20\div4=5
Since the base number is the same in each term, we can subtract the indices
10-5=5
This means
20 b^{10} \div 4 b^{5}=5 b^{5}
We need to divide the coefficients
42\div6=7
Since the base number is the same in each term, we can subtract the indices
-3- \,-8=-3+8=5
This means
42a^{-3} \div 6 a^{-8}=7 a^{5}
Anything raised to the power zero is 1 , so
(32 x)^{0}=1
This means we have
1\times6^{2}=1\times36=36
The negative index number indicates we need the reciprocal of
(5x)^{3}
Since
5x^{3}=5x\times5x\times5x=125x^{3}
We have
(5 x)^{-3}=\frac{1}{125 x^{3}}
The negative index number indicates we need the reciprocal of
b^{4}
The index number does not affect the 6 , hence
6 b^{-4}=\frac{6}{b^{4}}
The index number is telling us to square the cube root, so
64^{\frac{2}{3}}=(\sqrt[3]{64})^{2}=4^{2}=16
The index number is telling us to find the reciprocal of the square root, so
\begin{aligned} &16^{-\frac{1}{2}}\\ &=\frac{1}{16^{\frac{1}{2}}}\\ &=\frac{1}{\sqrt{16}}\\ &=\frac{1}{4} \end{aligned}
Laws of indices GCSE questions
1. Simplify
\frac{p^{7}}{p^{3}}
(1 mark)
Show answer
2. Simplify
6 h^{3} m^{6} \times 4 h^{4} m^{5}
(2 marks)
Show answer
h^{7} \text { or } m^{11} seen (evidence of adding powers)
(1)
24 h^{7} m^{11}
(1)
3. Simplify
\frac{12 x^{5} y^{7}}{3 x^{2} y}
(2 marks)
Show answer
x^{3} \text { or } y^{6} seen (evidence of subtracting powers)
(1)
4 x^{3} y^{6}
(1)
Learning checklist
You have now learned how to:
- Simplify expressions involving the laws of indices
- Calculate with roots, and with integer and fractional indices
Still stuck?
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Laws Of Indices Mathematics Pdf
Source: https://thirdspacelearning.com/gcse-maths/algebra/laws-of-indices/
Posted by: randallevould.blogspot.com
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