Consider the function f(x) = 4(1 ? e^x). (a) Find the exact slope of the graph of f(x) at the point where it crosses the x-axis. slope = (b) Find the exact equation of the tangent line to the graph of f(x) at the point in part (a). y(x) = (c) Find the exact equation of the line which is perpendicular to the tangent line in part (b). This line is called a normal line. y(x) =