Decompose the signal (1 + 0.1 cos5t) cos100t into a linear combination of sinusoidal functions, and find the amplitude, frequency, and phase of each component. Hint: use the identity for cosa cosb.

Respuesta :

Answer:

Given in explanation.

Explanation:

First seperate the signal into components,

[tex](1 + 0.1 \cos5t)\cos100t=\cos100t+0.1 \cos5t\cos100t[/tex]

Now, we will use the identity given in the hint,

[tex]\cos A \cos B = \frac{1}{2} (\cos(A+B) + \cos(A-B))\\\\\cos100t+0.1 \cos5t\cos100t=\cos100t + 0.05\cos105t + 0.05\cos95t[/tex]

Now the signal is decomposed into its different components.

Accordingly,

[tex]at\:\:100/(2*\pi) = 50/\pi \:Hz \:(16\:Hz)\:\:The \:\:amplitude\:\: is\:\: 1 \\at\:\:105/(2*\pi) = 52.5/\pi \:Hz \:(17\:Hz)\:\:The \:\:amplitude\:\: is\:\: 0.05 \\at\:\:95/(2*\pi) = 47.5/\pi \:Hz \:(15\:Hz)\:\:The \:\:amplitude\:\: is\:\: 0.05[/tex]

Since there  is no other term within the cos function, the phase differences in all of the above cases are zero.

The amplitude, frequency, and phase of each component are respectively;

Amplitude; 1, 0.05, 0.05

Frequency; 50/π, 52.5/π, 47.5/π

Phase; All are zero

We are given the signal;

(1 + 0.1 cos5t) cos100t

Expanding by multiplying out the bracket gives;

cos100t + 0.1 cos5t cos100t

From trigonometric identity, we know that;

cosA cosB = ¹/₂[cos(A + B) + cos(A - B)]

⇒ 0.5cos(A + B) + 0.5cos(A - B)

Thus;

cos100t + 0.1 cos5t cos100t = cos100t + 0.1[0.5cos(5t + 100t) + 0.5cos(5t - 100t)]

⇒  cos100t + 0.1[0.5cos(105t) - 0.5cos(95t)]

⇒  cos100t + 0.05cos(105t) - 0.05cos(95t)

We know that formula for simple harmonic motion is;

x(t) = Acos(ωt + φ)

where;

A is amplitude

ω is angular frequency

φ is phase angle

decomposing the signal equation gives;

cos100t

0.05cos(105t)

0.05cos(95t)

Comparing each with x(t) = Acos(ωt + φ), we have;

For cos100t;

A = 1

ω = 100

phase = 0

Frequency; f = ω/2π

f = 100/2π

f = 50/π

For 0.05cos(105t);

A = 0.05

ω = 105

phase = 0

Frequency; f = ω/2π

f = 105/2π

f = 52.5/π

For 0.05cos(95t);

A = 0.05

ω = 95

phase = 0

Frequency; f = ω/2π

f = 95/2π

f = 47.5/π

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