A linear function
we have seen is a function whose graph lies on a straight line, and which can be described by giving its slope and its y intercept
Linearity
If both system yield the same output function, this is called a linear system.
Prove
[1] y(t)=2x(t)
x1(t)--->[system]---->y1(t)=2x1(t)---->*a ---(1) a*2*x1(t)
x2(t)--->[system]---->y2(t)=2x2(t)---->*b ---(2) b*2*x2(t)
(1)+(2)= 2ax1(t)+2bx2(t)
[2] x1(t)--->*a --- (3) a*x1(t) x2(t)--->*b --- (4) b*x2(t)
(3)+(4)=a*x1(t)+b*x2(t) ---->[system]---->2(a*x1(t)+b*x2(t))=2ax1(t)+2bx1(t)
The results of [1] and [2] are the same. Thus, this is linear system.
