(1) Use the trigonometric identities for sin A sin B, sin A cos B, and cos A cos B to show that | sin(mæ) cos(næ) = 0 for any integer m, n, and | sin(mz) sin(nz) = (о, if m#n, | T, if m=n [0, if m ± n, | cos(mz) cos(nz) - %3D if m = n.

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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One very important application of Calculus is to Fourier theory, for example in
the field of signal processing (and many other places in physics and engineering).
The foundation of this is the fact that any (nice enough) periodic function f(x)
with period 27, meaning that f(x) = f(x + 27), can be expressed as a Fourier
series
ao
f(x) =
2
(an cos(nx) + b, sin(nx))
n=1
where ao, an, and b, are called the Fourier coefficients, that we shall calculate below.
(We will study series more intensively in Chapter 11, but for now we will assume
that this sum converges.)
(1) Use the trigonometric identities for sin A sin B, sin A cos B, and cos A cos B
to show that
sin(mx) cos(nx) = 0
for any integer m, n, and
о, if m#n,
| sin(ma) sin(næ) =
T,
if m = n
| cos (тa) сos(пa) :
0, if m + n,
if m %3D п.
(2) Now consider the integral
with f(x) as above. Use trigonometric integration and the Fourier series of
f(x) to show that
ao = -
(3) To find the remaining coefficients an and b, for n > 0, use the integrals
| f(x) cos
madx,
f(x) sin mædx
and Exercise 1 to show that
1
an =
1.
E f(2) cos(nz)dzr, b, =
E f(2) sin(nx)dz.
(4) Let's work out one simple example. Square waves are often encountered in
electronics and signal processing, particularly digital electronics and digital
signal processing. Consider the square wave with period 27,
(o, if – n< x <0
| 1, if 0 < x < T
f(x) =
Transcribed Image Text:One very important application of Calculus is to Fourier theory, for example in the field of signal processing (and many other places in physics and engineering). The foundation of this is the fact that any (nice enough) periodic function f(x) with period 27, meaning that f(x) = f(x + 27), can be expressed as a Fourier series ao f(x) = 2 (an cos(nx) + b, sin(nx)) n=1 where ao, an, and b, are called the Fourier coefficients, that we shall calculate below. (We will study series more intensively in Chapter 11, but for now we will assume that this sum converges.) (1) Use the trigonometric identities for sin A sin B, sin A cos B, and cos A cos B to show that sin(mx) cos(nx) = 0 for any integer m, n, and о, if m#n, | sin(ma) sin(næ) = T, if m = n | cos (тa) сos(пa) : 0, if m + n, if m %3D п. (2) Now consider the integral with f(x) as above. Use trigonometric integration and the Fourier series of f(x) to show that ao = - (3) To find the remaining coefficients an and b, for n > 0, use the integrals | f(x) cos madx, f(x) sin mædx and Exercise 1 to show that 1 an = 1. E f(2) cos(nz)dzr, b, = E f(2) sin(nx)dz. (4) Let's work out one simple example. Square waves are often encountered in electronics and signal processing, particularly digital electronics and digital signal processing. Consider the square wave with period 27, (o, if – n< x <0 | 1, if 0 < x < T f(x) =
Square wave
0.5
Time →
Use the preceding formulas to compute its Fourier series. (Hint: you should
split the integrals over [-7,T] into two integrals over [-T, 0] and [0, 1]
respectively over which the values of f(x) are constant.)
(5) Bonus: Graph the first 5 terms (or more) in the Fourier series of the square
wave to see how good of an approximates it.
Transcribed Image Text:Square wave 0.5 Time → Use the preceding formulas to compute its Fourier series. (Hint: you should split the integrals over [-7,T] into two integrals over [-T, 0] and [0, 1] respectively over which the values of f(x) are constant.) (5) Bonus: Graph the first 5 terms (or more) in the Fourier series of the square wave to see how good of an approximates it.
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