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There are two variable parameters in general:

- Amplitude
- Time

**The following operation can be performed with amplitude:**

C x(t) is a amplitude scaled version of x(t) whose amplitude is scaled by a factor C.

Addition of two signals is nothing but addition of their corresponding amplitudes. This can be best explained by using the following example:

As seen from the diagram above,

-10 < t < -3 amplitude of z(t) = x1(t) + x2(t) = 0 + 2 = 2

-3 < t < 3 amplitude of z(t) = x1(t) + x2(t) = 1 + 2 = 3

3 < t < 10 amplitude of z(t) = x1(t) + x2(t) = 0 + 2 = 2

subtraction of two signals is nothing but subtraction of their corresponding amplitudes. This can be best explained by the following example:

As seen from the diagram above,

-10 < t < -3 amplitude of z (t) = x1(t) - x2(t) = 0 - 2 = -2

-3 < t < 3 amplitude of z (t) = x1(t) - x2(t) = 1 - 2 = -1

3 < t < 10 amplitude of z (t) = x1(t) + x2(t) = 0 - 2 = -2

Multiplication of two signals is nothing but multiplication of their corresponding amplitudes. This can be best explained by the following example:

As seen from the diagram above,

-10 < t < -3 amplitude of z (t) = x1(t) ×x2(t) = 0 ×2 = 0

-3 < t < 3 amplitude of z (t) = x1(t) ×x2(t) = 1 ×2 = 2

3 < t < 10 amplitude of z (t) = x1(t) × x2(t) = 0 × 2 = 0

x(t $\pm$ t_{0}) is time shifted version of the signal x(t).

x (t + t_{0}) $\to$ negative shift

x (t - t_{0}) $\to$ positive shift

x(At) is time scaled version of the signal x(t). where A is always positive.

|A| > 1 $\to$ Compression of the signal

|A| < 1 $\to$ Expansion of the signal

Note: u(at) = u(t) time scaling is not applicable for unit step function.

x(-t) is the time reversal of the signal x(t).

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