4. (10 points) Compute the following, showing all the steps in your work. (a, 2 points) 1 (2 + sin(1 ) + 30 ) dt (b, 4 points) The value of a for which we can guarantee that f (x) = In (ax - 4x2 +2) has a hori- zontal tangent line in the range (0, 2). (c, 4 points) dy (xtan -' (x) )