9. Let f(x) = (1 +x2)-1. (a) Show that (1 +x2) f'(x) +xf(x) = 0. (b) Let n be a non-negative integer, show that (1 + x2) f( n+2) ( x) + (2n + 3)xf(n+1) (x) + (n + 1)2 f(n)(x) =0. (c) Hence, or otherwise, find the Taylor series of (1 + x?) ? at x = 0 up to the term rt