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