the formula i used for this was the cylindircal shell method:

\(\displaystyle

\)\(\displaystyle v=\int^b_{a} (2\pi{x}*f{(x)})dx

\)

So i evaluated the volume to be:

\(\displaystyle

\)\(\displaystyle v=\int^a_{0} (2\pi{x}*\sqrt{x})dx

\)

\(\displaystyle

\)\(\displaystyle v=\int^a_{0} (2\pi*{x}^{3/2})dx

\)

\(\displaystyle

\)\(\displaystyle v=\frac{4\pi*{x}^{5/2}}5

\)

\(\displaystyle

\)\(\displaystyle v=\frac{4\pi*{a}^{5/2}}5

\)

But my friend got the result :

\(\displaystyle

\frac{\pi{a}^{5/2}}{5}

\)

so where did i go wrong? Can i not use this method?