Class VII

Power of a power with integer bases

Lesson

We previously looked at expressions like $7^2\times7^3=7^{2+3}$72×73=72+3, but how should we deal with a power of a power?

Exploration

Consider the expression $\left(5^2\right)^3$(52)3. What is the resulting power of base $5$5? To find out, have a look at the expanded form of the expression:

$\left(5^2\right)^3$(52)3	$=$=	$\left(5^2\right)\times\left(5^2\right)\times\left(5^2\right)$(52)×(52)×(52)
	$=$=	$\left(5\times5\right)\times\left(5\times5\right)\times\left(5\times5\right)$(5×5)×(5×5)×(5×5)
	$=$=	$5\times5\times5\times5\times5\times5$5×5×5×5×5×5
	$=$=	$5^6$56

In the expanded form, we can see that we are multiplying six groups of $5$5 together. That is, $\left(5^2\right)^3=5^6$(52)3=56.

We can confirm this result using the index law of multiplication:

We know $\left(5^2\right)\times\left(5^2\right)\times\left(5^2\right)=5^{2+2+2}$(52)×(52)×(52)=52+2+2 which is equal to $5^6$56.

The index law for further powers

We can avoid having to write each expression in expanded form by using the power of a power law.

The power of a power law

For any base number $a$a, and any numbers $m$m and $n$n as powers,

$\left(a^m\right)^n=a^{m\times n}$(am)n=am×n

That is, when simplifying a term with a power that itself has a power:

Keep the same base
Find the product of the powers

Practice questions

Question 1

Express in simplified index form:

$\left(9^4\right)^3$(94)3

Question 2

Simplify using the index laws:

$\left(3^5\right)^3\times\left(3^2\right)^3$(35)3×(32)3

Question 3

Simplify, using the index laws:

$\left(2^3\right)^0\times\left(2^2\right)^3$(23)0×(22)3

Outcomes

7.NS.P.2

Laws of exponents (through observing patterns to arrive at generalisation.) (i) a^m .a^n = a^(m+n) (ii) (a^m)^n = a^mn (iii) a^m / a^n = a^ (m-n) where m - n a member of N