This section is tricky as negative numbers always tend to be. The most important thing you will learn here is: \begin{lawbox} \large \[a^{-n} = \frac{1}{a^n}\] \end{lawbox} I want you to take a second to realise that this \fuzzyfont{breaks} your interpretation of $a$ being raised to some power $n$ as being $n$ successive multiplications of the number $a$. \[a^n = \underbrace{a \times a \times a \ldots}_{n} \] Suddenly what does it mean to multiply $a$ by itself \textit{$-n$} times?! Here is some working out space for you to reconcile with this fact. \begin{solutionorbox}[2in] \textbf{Proof:} Consider the product of \( a^n \) and \( a^{-n} \): \[ a^n \cdot a^{-n} = a^{n + (-n)} = a^0 \] Since anything raised to the power of 0 is 1, we have: \[ a^0 = 1 \] Therefore: \[ a^n \cdot a^{-n} = 1 \] Dividing both sides by \( a^n \), we get: \[ \frac{a^n \cdot a^{-n}}{a^n} = \frac{1}{a^n} \] Simplifying the left side, we have: \[ a^{-n} = \frac{1}{a^n} \] Hence proved. \end{solutionorbox} \begin{examplebox} \subsection{Examples:} \begin{questions} \item[Worked Example:] \[2^{-3} = \frac{1}{2^3} = \frac{1}{8}\] \Question[4] Evaluate \begin{parts}\begin{multicols}{2} \part \(6^{-2}\) \begin{solutionordottedlines}[2cm] \(6^{-2}=\frac{1}{6^{2}}\) \(=\frac{1}{36}\) \end{solutionordottedlines} \part \(4^{-3}\) \begin{solutionordottedlines}[2cm] \(4^{-3}=\frac{1}{4^{3}}\) \(=\frac{1}{64}\) \end{solutionordottedlines} \part \(2^{-7}\) \begin{solutionordottedlines}[2cm] \(2^{-7}=\frac{1}{2^{7}}\) \(=\frac{1}{128}\) \end{solutionordottedlines} \part \(10^{-3}\) \begin{solutionordottedlines}[2cm] \(10^{-3}=\frac{1}{10^{3}}\) \(=\frac{1}{1000}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[3] These ones just reciprocate! \begin{parts}\begin{multicols}{3} \part \(\left(\frac{1}{3}\right)^{-1}\) \begin{solutionordottedlines}[3cm] \(\left(\frac{1}{3}\right)^{-1}=\frac{3}{1}\) \(=3\) \end{solutionordottedlines} \part \(\left(\frac{2}{7}\right)^{-2}\) \begin{solutionordottedlines}[3cm] \(\left(\frac{2}{7}\right)^{-2}=\left(\frac{7}{2}\right)^{2}\) \(=\frac{49}{4}\) \end{solutionordottedlines} \part \(\left(4 \frac{1}{4}\right)^{-2}\) \begin{solutionordottedlines}[3cm] \(\left(4 \frac{1}{4}\right)^{-2}=\left(\frac{17}{4}\right)^{-2}\) \(=\left(\frac{4}{17}\right)^{2}\) \(=\frac{16}{289}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[8] Write as a single power and then evaluate: \begin{parts} \part \(3^{4} \times 3^{-2}\) \begin{solutionordottedlines}[2cm] \(3^{4} \times 3^{-2}=3^{2}\) \end{solutionordottedlines} \part \(5^{7} \times 5^{-8}\) \begin{solutionordottedlines}[2cm] \(5^{7} \times 5^{-8}=5^{-1}\) \[ =9 \] \end{solutionordottedlines} \part \(13^{-8} \times 13^{15} \times 13^{-7}\) \begin{solutionordottedlines}[2cm] \(\begin{aligned} 13^{-8} \times 13^{15} \times 13^{-7} & =13^{0} \\ & =1\end{aligned}\) \[ =1 \] \[ =\frac{1}{5} \] \end{solutionordottedlines} \part \(\left(\frac{2}{3}\right)^{-6} \times\left(\frac{2}{3}\right)^{4}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{2}{3}\right)^{-6} \times\left(\frac{2}{3}\right)^{4}=\left(\frac{2}{3}\right)^{-2}\) \[ =\left(\frac{3}{2}\right)^{2} \] \[ =\frac{9}{4} \] \end{solutionordottedlines} \begin{multicols}{2} \part \[\frac{2^{4}}{2^{5}}\] \begin{solutionordottedlines}[4cm] \(\frac{2^{4}}{2^{5}}=2^{-1}\) \(=\frac{1}{2}\) \end{solutionordottedlines} \part \[\frac{3^{4}}{3^{7}}\] \begin{solutionordottedlines}[4cm] \(\frac{3^{4}}{3^{7}}=3^{-3}\) \(=\frac{1}{3^{3}}\) \(=\frac{1}{27}\) \end{solutionordottedlines} \part \[\frac{5}{5^{3}}\] \begin{solutionordottedlines}[4cm] \(\frac{5}{5^{3}}=5^{-2}\) \(=\frac{1}{5^{2}}\) \(=\frac{1}{25}\) \end{solutionordottedlines} \part \[\frac{3^{4}}{3^{6}}\] \begin{solutionordottedlines}[4cm] \(\frac{3^{4}}{3^{6}}=3^{-2}\) \(=\frac{1}{3^{2}}\) \(=\frac{1}{9}\) \end{solutionordottedlines} \end{multicols} \end{parts} \Question[4] Simplify, expressing the answers with positive indices \begin{parts}\begin{multicols}{2} \part \(a^{2} b^{-3} \times a^{-4} b^{5}\) \begin{solutionordottedlines}[3cm] \(a^{2} b^{-3} \times a^{-4} b^{5}=a^{2-4} \times b^{-3+5}\) \(=\frac{1}{a^{2}} \times b^{2}\) \(=\frac{b^{2}}{a^{2}}\) \end{solutionordottedlines} \part \(\frac{x^{2} y^{3}}{x^{3} y^{2}}\) \begin{solutionordottedlines}[3cm] \(\frac{x^{2} y^{3}}{x^{3} y^{2}}=x^{-1} y^{1}\) \(=\frac{1}{x} \times y\) \(=\frac{y}{x}\) \end{solutionordottedlines} \part \(\left(2 a^{-2} b^{3}\right)^{-2}\) \begin{solutionordottedlines}[3cm] \(\left(2 a^{-2} b^{3}\right)^{-2}=2^{-2} \times a^{4} \times b^{-6}\) \(=\frac{1}{2^{2}} \times a^{4} \times \frac{1}{b^{6}}\) \(=\frac{a^{4}}{4 b^{6}}\) \end{solutionordottedlines} \part \(\left(\frac{3 m^{2}}{n}\right)^{-4}\) \begin{solutionordottedlines}[3cm] \(\left(\frac{3 m^{2}}{n}\right)^{-4}=\left(\frac{n}{3 m^{2}}\right)^{4}\) \(=\frac{n^{4}}{81 m^{8}}\) \end{solutionordottedlines} \end{multicols}\end{parts} \end{questions} \end{examplebox} \fbox{\fbox{\parbox{\textwidth}{Note that in general \(\left(\frac{a}{b}\right)^{-1}=\frac{b}{a}\). }}} \begin{exercisebox} \subsection{Exercises:} \begin{questions} \Question[4] Express with a positive index and then evaluate. \begin{parts}\begin{multicols}{2} \part \(2^{-1}\) \begin{solutionordottedlines}[2cm] \(2^{-1} = \frac{1}{2}\)\\ \(2^{-1} = 0.5\) \end{solutionordottedlines} \part \(5^{-1}\) \begin{solutionordottedlines}[2cm] \(5^{-1} = \frac{1}{5}\)\\ \(5^{-1} = 0.2\) \end{solutionordottedlines} \part \(2^{-4}\) \begin{solutionordottedlines}[2cm] \(2^{-4} = \frac{1}{2^4}\)\\ \(2^{-4} = 0.0625\) \end{solutionordottedlines} \part \(3^{-3}\) \begin{solutionordottedlines}[2cm] \(3^{-3} = \frac{1}{3^3}\)\\ \(3^{-3} = \frac{1}{27}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4] Write each fraction as a power of a prime with a negative index. \begin{parts}\begin{multicols}{2} \part \(\frac{1}{8}\) \begin{solutionordottedlines}[2cm] \(\frac{1}{8} = 2^{-3}\) \end{solutionordottedlines} \part \(\frac{1}{9}\) \begin{solutionordottedlines}[2cm] \(\frac{1}{9} = 3^{-2}\) \end{solutionordottedlines} \part \(\frac{1}{16}\) \begin{solutionordottedlines}[2cm] \(\frac{1}{16} = 2^{-4}\) \end{solutionordottedlines} \part \(\frac{1}{64}\) \begin{solutionordottedlines}[2cm] \(\frac{1}{64} = 2^{-6}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4] Express with positive indices, evaluating where possible. \begin{parts}\begin{multicols}{2} \part \(a^{-3}\) \begin{solutionordottedlines}[2cm] \(a^{-3} = \frac{1}{a^3}\) \end{solutionordottedlines} \part \(x^{-7}\) \begin{solutionordottedlines}[2cm] \(x^{-7} = \frac{1}{x^7}\) \end{solutionordottedlines} \part \(\frac{3}{a^{-4}}\) \begin{solutionordottedlines}[2cm] \(\frac{3}{a^{-4}} = 3a^4\) \end{solutionordottedlines} \part \(\frac{5}{x^{-5}}\) \begin{solutionordottedlines}[2cm] \(\frac{5}{x^{-5}} = 5x^5\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4] Simplify and then evaluate \begin{parts}\begin{multicols}{2} \part \(\left(\frac{1}{4}\right)^{-1}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{1}{4}\right)^{-1} = 4\) \end{solutionordottedlines} \part \(\left(\frac{2}{5}\right)^{-2}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{2}{5}\right)^{-2} = \left(\frac{5}{2}\right)^2\)\\ \(\left(\frac{2}{5}\right)^{-2} = \frac{25}{4}\) \end{solutionordottedlines} \part \(3^{5} \times 3^{-2}\) \begin{solutionordottedlines}[2cm] \(3^{5} \times 3^{-2} = 3^{5-2}\)\\ \(3^{5} \times 3^{-2} = 3^3\)\\ \(3^{5} \times 3^{-2} = 27\) \end{solutionordottedlines} \part \(5^{11} \times 5^{-8}\) \begin{solutionordottedlines}[2cm] \(5^{11} \times 5^{-8} = 5^{11-8}\)\\ \(5^{11} \times 5^{-8} = 5^3\)\\ \(5^{11} \times 5^{-8} = 125\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4]$\,$ \begin{parts}\begin{multicols}{2} \part \(\frac{2^{3}}{2^{6}}\) \begin{solutionordottedlines}[2cm] \(\frac{2^{3}}{2^{6}} = 2^{3-6}\)\\ \(\frac{2^{3}}{2^{6}} = 2^{-3}\)\\ \(\frac{2^{3}}{2^{6}} = \frac{1}{8}\) \end{solutionordottedlines} \part \(\frac{4^{2}}{4^{4}}\) \begin{solutionordottedlines}[2cm] \(\frac{4^{2}}{4^{4}} = 4^{2-4}\)\\ \(\frac{4^{2}}{4^{4}} = 4^{-2}\)\\ \(\frac{4^{2}}{4^{4}} = \frac{1}{16}\) \end{solutionordottedlines} \part \(\frac{8^{6}}{8^{7}}\) \begin{solutionordottedlines}[2cm] \(\frac{8^{6}}{8^{7}} = 8^{6-7}\)\\ \(\frac{8^{6}}{8^{7}} = 8^{-1}\)\\ \(\frac{8^{6}}{8^{7}} = \frac{1}{8}\) \end{solutionordottedlines} \part \(\frac{20^{4}}{20^{6}}\) \begin{solutionordottedlines}[2cm] \(\frac{20^{4}}{20^{6}} = 20^{4-6}\)\\ \(\frac{20^{4}}{20^{6}} = 20^{-2}\)\\ \(\frac{20^{4}}{20^{6}} = \frac{1}{400}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[3] Express with negative index. \begin{parts}\begin{multicols}{3} \part \(\frac{3}{x}\) \begin{solutionordottedlines}[2cm] \(\frac{3}{x} = 3x^{-1}\) \end{solutionordottedlines} \part \(\frac{5}{x^{2}}\) \begin{solutionordottedlines}[2cm] \(\frac{5}{x^{2}} = 5x^{-2}\) \end{solutionordottedlines} \part \(\frac{8}{x^{4}}\) \begin{solutionordottedlines}[2cm] \(\frac{8}{x^{4}} = 8x^{-4}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[3] Evaluate. \begin{parts}\begin{multicols}{3} \part \(\left(\frac{1}{2}\right)^{-1}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{1}{2}\right)^{-1} = 2\) \end{solutionordottedlines} \part \(\left(\frac{2}{3}\right)^{-1}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{2}{3}\right)^{-1} = \frac{3}{2}\) \end{solutionordottedlines} \part \(\left(\frac{1}{2}\right)^{-2}\) \begin{solutionordottedlines}[2cm] \(\left(\frac{1}{2}\right)^{-2} = 2^2\)\\ \(\left(\frac{1}{2}\right)^{-2} = 4\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4] Simplify, expressing the answer with positive indices. \begin{parts}\begin{multicols}{2} \part \(x^{-6} y^{4} \times x^{2} y^{-2}\) \begin{solutionordottedlines}[2cm] \(x^{-6} y^{4} \times x^{2} y^{-2} = x^{-6+2} y^{4-2}\)\\ \(x^{-6} y^{4} \times x^{2} y^{-2} = x^{-4} y^{2}\)\\ \(x^{-6} y^{4} \times x^{2} y^{-2} = \frac{y^2}{x^4}\) \end{solutionordottedlines} \part \(2 a^{-1} b^{5} \times 7 a b^{-3}\) \begin{solutionordottedlines}[2cm] \(2 a^{-1} b^{5} \times 7 a b^{-3} = 14 a^{-1+1} b^{5-3}\)\\ \(2 a^{-1} b^{5} \times 7 a b^{-3} = 14 b^{2}\) \end{solutionordottedlines} \part \(\frac{8 a^{-4}}{2 a^{6}}\) \begin{solutionordottedlines}[2cm] \(\frac{8 a^{-4}}{2 a^{6}} = 4 a^{-4-6}\)\\ \(\frac{8 a^{-4}}{2 a^{6}} = 4 a^{-10}\)\\ \(\frac{8 a^{-4}}{2 a^{6}} = \frac{4}{a^{10}}\) \end{solutionordottedlines} \part \(\frac{36 h^{-9}}{9 h^{-4}}\) \begin{solutionordottedlines}[2cm] \(\frac{36 h^{-9}}{9 h^{-4}} = 4 h^{-9+4}\)\\ \(\frac{36 h^{-9}}{9 h^{-4}} = 4 h^{-5}\)\\ \(\frac{36 h^{-9}}{9 h^{-4}} = \frac{4}{h^{5}}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[6] Fill in the missing term \begin{parts}\begin{multicols}{2} \part \(6^{4} \times \ldots=6^{2}\) \begin{solutionordottedlines}[2cm] \(6^{4} \times 6^{-2} = 6^{2}\) \end{solutionordottedlines} \part \(m^{5} \times \ldots=m^{-6}\) \begin{solutionordottedlines}[2cm] \(m^{5} \times m^{-11} = m^{-6}\) \end{solutionordottedlines} \part \(d^{-7} \div \ldots=d^{15}\) \begin{solutionordottedlines}[2cm] \(d^{-7} \div d^{-22} = d^{15}\) \end{solutionordottedlines} \part \(\left(a^{5}\right) \cdots=a^{-15}\) \begin{solutionordottedlines}[2cm] \(\left(a^{5}\right)^{-3} = a^{-15}\) \end{solutionordottedlines} \part \((\ldots)^{-2}=\frac{m^{6}}{25}\) \begin{solutionordottedlines}[2cm] \((\frac{m^{3}}{5})^{-2} = \frac{m^{6}}{25}\) \end{solutionordottedlines} \part \((\ldots)^{-2}=p^{4} q^{-6}\) \begin{solutionordottedlines}[2cm] \((p^{2} q^{-3})^{-2} = p^{4} q^{-6}\) \end{solutionordottedlines} \end{multicols}\end{parts} \Question[4] Simplify, expressing the answers with positive indices. Evaluate powers where possible. \begin{parts}\begin{multicols}{2} \part \(\left(3 a^{2} b^{-2}\right)^{3} \times\left(2 a^{4}\right)^{-2}\) \begin{solutionordottedlines}[2cm] \(\left(3 a^{2} b^{-2}\right)^{3} \times\left(2 a^{4}\right)^{-2} = 27 a^{6} b^{-6} \times \frac{1}{4 a^{8}}\)\\ \(\left(3 a^{2} b^{-2}\right)^{3} \times\left(2 a^{4}\right)^{-2} = \frac{27}{4} a^{-2} b^{-6}\)\\ \(\left(3 a^{2} b^{-2}\right)^{3} \times\left(2 a^{4}\right)^{-2} = \frac{27}{4 a^{2} b^{6}}\) \end{solutionordottedlines} \part \(\left(6 a^{5} b^{-4}\right)^{-3} \times 2\left(a^{3} b^{-3}\right)^{2}\) \begin{solutionordottedlines}[2cm] \(\left(6 a^{5} b^{-4}\right)^{-3} \times 2\left(a^{3} b^{-3}\right)^{2} = \frac{1}{216 a^{15} b^{-12}} \times 2 a^{6} b^{-6}\)\\ \(\left(6 a^{5} b^{-4}\right)^{-3} \times 2\left(a^{3} b^{-3}\right)^{2} = \frac{2}{216} a^{-9} b^{6}\)\\ \(\left(6 a^{5} b^{-4}\right)^{-3} \times 2\left(a^{3} b^{-3}\right)^{2} = \frac{1}{108 a^{9} b^{6}}\) \end{solutionordottedlines} \part \(\frac{\left(2 a^{4} b^{-2}\right)^{3}}{c^{2}} \times \frac{\left(2^{2} a^{-3} b^{2}\right)^{-1}}{c}\) \begin{solutionordottedlines}[2cm] \(\frac{\left(2 a^{4} b^{-2}\right)^{3}}{c^{2}} \times \frac{\left(2^{2} a^{-3} b^{2}\right)^{-1}}{c} = \frac{8 a^{12} b^{-6}}{c^{2}} \times \frac{c}{4 a^{3} b^{-2}}\)\\ \(\frac{\left(2 a^{4} b^{-2}\right)^{3}}{c^{2}} \times \frac{\left(2^{2} a^{-3} b^{2}\right)^{-1}}{c} = \frac{2 a^{9} b^{-4}}{c^{3}}\) \end{solutionordottedlines} \part \(\mathbf{j} \frac{\left(2 a^{4}\right)^{2}}{b^{7}} \div \frac{\left(a^{2}\right)^{-3}}{2 b}\) \begin{solutionordottedlines}[2cm] \(\mathbf{j} \frac{\left(2 a^{4}\right)^{2}}{b^{7}} \div \frac{\left(a^{2}\right)^{-3}}{2 b} = \mathbf{j} \frac{4 a^{8}}{b^{7}} \times \frac{2 b}{a^{-6}}\)\\ \(\mathbf{j} \frac{\left(2 a^{4}\right)^{2}}{b^{7}} \div \frac{\left(a^{2}\right)^{-3}}{2 b} = \mathbf{j} \frac{8 a^{14}}{b^{6}}\) \end{solutionordottedlines} \end{multicols}\end{parts} \end{questions} \end{exercisebox}