we can see that f(r) is continuous on the open interval (—1, oo). In the limit as r approaches —1 from the right, the function values approach positive infinity. On the other hand as r approaches positive infinity, the function values approach — P < 0 asymptotically. Thus by the Intermediate Value Theorem (p. 108 of [Smith and Minton (2002)]) there exists r* with -1 < r* < oo such that f(r*) = 0. The reader is encouraged to show that r* is unique in the exercises