Consider the equation ru" (r)+u'(r) = 0. a) Show that the set of functions V = { : R R : r f" (r) + f(r) = 0} is a vector space. b) Verify by direct substitution that f(r) = 1 and f(r) = lnr solve (2). c) Using the preceding parts, find a solution u(r) of (2) satisfying u(1) u(2) = 2. = 1 and