ddt[e−ρtU′(C)]=e−ρtU′(C)r\dfrac{d}{dt}\bigl[e^{-\rho t}U'(C)\bigr] = e^{-\rho t}U'(C) rdtd[e−ρtU′(C)]=e−ρtU′(C)r. When is c˙>0\dot c > 0c˙>0?
r<ρr < \rhor<ρ \quad
r>ρr > \rhor>ρ \quad
r=ρr = \rhor=ρ \quad
Never.
