PROBLEMS 49 Problems 2.1 Consider the memoryless systems with characteristics shown in Fig. 2.18, in which u denotes the input and y the output. Which of them is a linear system? Is it possible to introduce a new output so that the system in Fig. 2.18 (b) is linear? FIGURE 2.18 y yo y y 0 0 (a) (b) (c)