SIGNALS AND SYSTEM
A SIGNAL is defined as any physical quantity that changes with time, distance, speed, position, pressure, temperature or some other quantity. A SIGNAL is physical quantity that consists of many sinusoidal of different amplitudes and frequencies.
x(t) = 10t
X(t) = 5x2+20xy+30y
A System is a physical device that performs an operations or processing on a signal. Ex Filter or Amplifier.