Derive the equation for time constant τ in step (c) above. Hint: Substitute each of the two data points [t1, Vo(t1)] and [t1, Vo(t2)] into the envelope function Env (t)= Vo ([infinity] ) + [ A - Vo ([infinity] )] e–t/τ to form two equations. Divide one equation by the other (side by side), simplify, take the natural log of the result, and solve for τ. Note that Env (t1) = Vo(t1) and Env (t2) = Vo(t2).