The equation of continuity in logarithmic differential form is d(In PAV) = 0; or d'Inp) + d(In A) + d(In V) = 0
1) Euler's equation of motion for an inviscid fluid is
dp = -pV dV
2) Assume an isentropic process and use an appropriate differential equation for speed of sound squared. Using these two equations show that pressure always decreases in an accelerating flow and increases in a decelerating flow via an inequality for dV /dp, where your result only involves V and p.