Question

A continuous time LTI system has memory only when __________

(a) It does not depend on the present value of the input

(b) It only depends on the past values of the input

(c) Its output always depends both on the previous and past values of the input

(d) Its output might depend on the present value as well as the previous value of the input

I have been asked this question by my college director while I was bunking the class.

This question is from Properties of LTI Systems in section Time-Domain Analysis of CT Systems of Signals and Systems

Answer 1

Right choice is (d) Its output might depend on the present value as well as the previous value of the input

To elaborate: An LTI system is said to have a memory when its output at any time depends on the previous value of the input. This does not mean its value does not depend on present values. It depends both on past and present values according to the situation.