Consider the two-dimensional incompressible velocity potential = xy + x2 y2. (a) Is it true that

Consider the two-dimensional incompressible velocity potential φ = xy + x2 – y2. (a) Is it true that ∆2φ = 0, and, if so, what does this mean? (b) If it exists, find the stream function ψ(x, y) of this flow. (c) Find the equation of the streamline which passes through (x, y) = (2, 1).