A system is linear if:
A system for any constants e, j ect.. and for any input x1[t], x2[t] or x1(t), x2(t)
has the output y1[t], y2[t] or y1(t), y2(t) relative to
ax1(t) + bx2(t) is ay1(t) + by2(t)
Or more easily understood, if both systems give the same output for any
x1[t],x2[t], a, b then the system is linear. So if you add two input and then send them through the system the system's output should be equivalent to what is gotten when the two inputs go through the system separately and then are added.
A non linear system:
A system is non linear if it doesn't match the requirements for a linear system.
For instance when two inputs are added then sent through the system the output does not equal two separate signals going through the same system and then being added.
