Looks great, q_fruit! Perhaps they just wrote it differently?
\(\displaystyle \L -\frac{1}{3}(3 - 2s)^{\frac{3}{2}} \, + \, C\)
or
\(\displaystyle \L -\frac{1}{3}\sqrt{(3 - 2s)^3 \, } \, + \, C\)
or
\(\displaystyle \L -\frac{(3 - 2s)^{\frac{3}{2}}}{3} \, + \, C\)
or
\(\displaystyle \L -\frac{\sqrt{(3 - 2s)^3 \, }}{3} \, + \, C\)
That's me out of ideas.