Hello so I have the following code:
\underline{Example:} Use mathematical induction to prove that for every integer $n \ge 0$: [
P(n): \quad \sum_{j = 0}^n \parens{-\f12}^j = \f{2^{n+1} + (-1)^n}{3\cdot 2^n}]
\underline{Basis step:} We verify $\map P 0$ is true.
[ \map P 0: \quad 1 = \f{2^{0+1}+(-1)^0}{3\cdot 2^0} = \f{2+1}{3} = 1 \implies \map P 0 \textsx{is true}]
\underline{Inductive step:} We will assume:
\begin{align*}
\map P k: \sum_{j = 0}^k \parens{-\f12}^j &= \f{2^{k+1} + (-1)^k}{3\cdot 2^k} \textsx{is true} \
\text{We want to show} \
\map P{k+1}: \sum_{j=0}^{k+1} \parens{-\f12}^j &= \f{2^{k+2} + (-1)^{k+1}}{3\cdot 2^{k+1}} \
\text{And by the inductive hypothesis}\
\map P{k+1}: \sum_{j=0}^{k+1} \parens{-\f12}^j &= \f{2^{k+1} + (-1)^k}{3\cdot 2^k} + \parens{-\f12}^{k+1} = \f{2^{k+1} + (-1)^k}{3\cdot 2^k} + \f{(-1)^{k+1}}{2^{k+1}} \
&= \f{2^{k+2} +2(-1)^k + 3(-1)(-1)^k}{3\cdot 2^{k+1}} = \f{2^{k+2} +(2-3)(-1)^k}{3\cdot 2^{k+1}} \
&= \f{2^{k+2}+(-1)(-1)^k}{3\cdot 2^{k+1}} = \f{2^{k+2}+(-1)^{k+1}}{3\cdot 2^{k+1}}
\end{align*}