$10\mathrm{.}4$ In polar coordinates, the continuity equation for steady, incompressible flow becomes

$\frac{1}{r}\frac{\text{d}\text{e}\text{l}}{\text{d}\text{e}\text{l}\text{r}}(r{v}_r)+\frac{1}{r}\frac{del{v}_{}}{\text{d}\text{e}\text{l}}=0$

Derive equations $(10-10),$ using this relation.

a$.=v_{}L[(\frac{x}{L}{)}^3-\frac{3x{y}^2}{L^3}]$

b$.=v_{}\frac{xy}{L}$

c$.=\frac{v_{}L}{2}ln(x^2+y^2)$