By direct computation, check that the function u(x) = $|x|^{1/2}$ cos($\theta$/2) is harmonic in the upper half plane H := {x = (x1, x2) | x2 > 0}.

Question

Okay so Partial Differential Equations make no sense to me. Don't know what to do. All I know is that if a function u is harmonic then $\Delta$u = 0