Proof n^2 - 4n = Big-Theta(2^n)
<p>I should prove or disprove the equation<br>
    n^2 - 4n = Big-Theta(2^n)</p>

<p>As far as i know i need to prove the following two equations:</p>

<pre><code>f = O(g)
g = O(f)
</code></pre>

<p>I started to solve f = O(g)</p>

<pre><code>n^2 - 4n = c * 2^n // use log
2log(n) - log(4n) = log(c) * n * log(2)
2log(n) - (log(4) + log(n)) = log(c) * n //log(2) at base 2 is 1
</code></pre>

<p>But how do i continue from here on?</p>