Suppose that u = x 2 + y z , x = ρ r cos ( θ ) , y = ρ r sin ( θ ) {\displaystyle \displaystyle u=x^{2}+yz,\ x=\rho r\cos(\theta ),\ y=\rho r\sin(\theta )} and z = ρ r {\displaystyle \displaystyle z=\rho r} . Find ∂ u ∂ r {\displaystyle \displaystyle {\frac {\partial u}{\partial r}}} at the point ( ρ 0 , r 0 , θ 0 ) = ( 2 , 3 , π / 2 ) {\displaystyle \displaystyle (\rho _{0},r_{0},\theta _{0})=(2,3,\pi /2)} .
and 
. Find 
at the point 
.
