I have a conceptual question about fluid... we derive the equations about pressure in fluid by considering the mass above a particular point in fluid. and for fluid at rest, the pressure above equals pressure from below. how about on the perpendicular plane? is the pressure on the sides equal to pressure from above and below also? my textbook says that 'At any point in a fluid at rest, the pressure is the same in all directions at a given depth', is it an experimental statement or can it be shown mathematically?