Linear Systems
According to what I have understood, If a system input x(t) produces and output y(t), then it follows that if the system input is x(t+d) then output will be y(t+d). Also another idea is, If x1(t) --> y1(t) and x2(t) --> y2(t), then it follows that the input to the same system a1.x1(t)+a2.x2(t) gives output a1y1(t)+ a2y2(t)
Example of a Linear System
Given the system y(t) = 2x(t)
Input x1(t) = 4n and x2(t) = 10, we get y1(t) = 8n and y2(t) = 20. y1(t) + y2(t) = 8n+20
Input sum of the two inputs x(t) = 4n + 10, we get output y3(t) = 8n+20.
So--> y1(t) + y2(t) = y3(t) the system is LINEAR.