4)
a) dv/(v+17) = -2 dt so integrating on both sides yields ln(v+17) = -2t + c. exponentiate both sides to get v in terms of t, then use the initial condition to get a particular solution. i get v = 30exp(-2t) - 17.
b) exp(-2t) tends to 0 as t tends to infinity, so the answer is -17.
c) solve v(t) = 20 for t.
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