Consider a series RL circuit with a voltage source. Take the output as the voltage across the resistor with L = 2 henrys and R = 4 ohms. (a) Find the zero input response as a function of time. The initial current is 2 A. (b) Determine the integrating factor for the differential equation relating output voltage to the input voltage source. (c) Now let the initial current be zero and determine an expression for the output response when the voltage source is a unit step function. (d) Now let the initial current be zero and determine an expression for the output response when the voltage source is an impulse function in which the spike occurs at time zero. . (e) Now let the initial current be zero and determine an expression for the output response when the voltage source is u(t).