4. for each of the following functions, indicate at which point(s) the function is discontinuous and explain which of the conditions of definition 4.3 is not satisfied. in each case, graph the function. (the domain is r in each case.) (a) (b) (c) (d) - 3x + 12, x 4 f(x) = 1/2x f(x) = 1/(x – b)2 for b constant f(x) = (x – 1)/(x2 + 2x – 3) [hint: factor the denominator.]