The open-loop DC gain of a unity negative feedback system with closed loop transfer function   is ____Select one:a. 9b. 4c. 4/13d. 4/9

To find the open-loop DC gain of a unity negative feedback system with a closed-loop transfer function, we need to evaluate the value of the transfer function at DC (zero frequency).

The open-loop transfer function is given by the product of the plant transfer function and the controller transfer function. In this case, since we have a unity negative feedback system, the closed-loop transfer function is equal to the product of the open-loop transfer function and 1/(1 + open-loop transfer function).

To find the open-loop DC gain, we substitute s = 0 into the closed-loop transfer function and simplify the expression.

Let's denote the closed-loop transfer function as H(s). Evaluating H(s) at s = 0, we have:

H(0) = open-loop transfer function(0) / (1 + open-loop transfer function(0))

Since the open-loop transfer function is not provided in the question, we cannot directly calculate the open-loop DC gain. Therefore, none of the given options (a. 9, b. 4, c. 4/13, d. 4/9) can be determined as the correct answer without additional information.