The following limit represents f'(a) for some function f and some value of a. 81+h-81 lim h0 h a. Find a function f and a number a. b. Determine the value of the limit by finding f'(a). a. f(x)= (Type an expression using x as the variable. Type an exact answer, using radicals as needed.) a= (Type an integer or a decimal.) b. f'(a)= (Type an exact answer, using radicals as needed.)