Thursday, November 4, 2021
Prove that for every natural number n, \(2^n+1 \leq 3^n \)
We will prove that for \(n \in \mathbb{N}, 2^n+1 \leq 3^n \) by induction.
First we will set up a base case at
\[
\begin{align}
n&=1\\
2^1+1&=3\\
3^1&=3\\
so \ 2^1+1 &\leq 3^1
\end{align}
\]
Since this base case holds we will move on to the induction step and assume that for some
\( n \in \mathbb{N}, \ 2^n+1 \leq 3^n \), and will show that this implies that \(2^{n+1}+1 \leq 3^{n+1}\)
\[
\begin{align}
2^{n+1}+1 &= (2*2^n)+1\\
&= 2(2^n+1)-1\\
&=((2^n+1)+(2^n+1))-1\\
&\leq 3^n+3^n-1\\
&=3^{n+1}-1-(3^n)\\
&\leq3^{n+1}
\end{align}
\]
So, by induction, for every \(n \in \mathbb{N}, 2^n+1 \leq 3^n\).
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