<p>You're write. There's a typo. This:</p>
<p>x^2 - 1/3 x^3 + 1/2 mx^2 = 1/2 (2 - m) x^2 - 1/3 x^3.</p>
<p>Should read this:</p>
<p>x^2 - 1/3 x^3 - 1/2 mx^2 = 1/2 (2 - m) x^2 - 1/3 x^3.</p>
<p>And then the two sides are equal. What's more, the left side is the actual antiderivative, whereas in the first line the left side of the equation is not.</p>
<p>Good catch, Latency. Nice.</p>