Derive an expression for change in entropy across an oblique shock wave, as a function of upstream Mach number and deflection angle.
a. ( Δ S = ln(M₂/M₁) + θ)
b. ( Δ S = ln(M₁/M₂) + θ)
c. ( Δ S = θ - ln(M₁/M₂))
d. ( Δ S = θ - ln(M₂/M₁))