how to obtain the laplacian in cylindrical coordinates?

[gjfelix2001]

i need a hint to obtain the laplacian in cylindrical coordinates. Thnkx

 

[main_road]

x=r*cos(θ), y=r*sin(θ).
Then use chain rule:
du/dx=(du/dr)*(dr/dx) + (du/dθ)*(dθ/dx)
du/dy=(du/dr)*(dr/dy) + (du/dθ)*(dθ/dy)
and then the second derivatives ...

Δu=(1/r)*d(r(du/dr))/dr +(1/r²)*d²u/dθ² +d²u/dz²