solucionario parte 5 matemáticas avanzadas para ingeniería - 2da edición - glyn james
TRANSCRIPT
5
The Fourier Transform
Exercises 5.2.4
1F (jω) =
∫ 0
−∞eate−jωt dt +
∫ ∞
0e−ate−jωt dt
=2a
a2 + ω2
2
F (jω) =∫ 0
−T
Ae−jωt dt +∫ T
0−Ae−jωt dt
=∫ T
02jA sinωt dt
=2jA
ω(1 − cos ωT )
=4jA
ωsin2 ωT
2
= jωAT 2 sinc2(
ωT
2
)
3
F (jω) =∫ 0
−T
(At
T+ A
)e−jωt dt +
∫ T
0
(−At
T+ A
)e−jωt dt
= 2∫ T
0
(−At
T+ A
)cos ωt dt
= AT sinc2(
ωT
2
)
Exercise 2 is T × derivative of Exercise 3, so result 2 follows as (jω × T )× result 3.
Sketch is readily drawn.
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4
F (jω) =∫ 2
−22Ke−jωt dt = 8K sinc(2ω)
G(jω) =∫ 1
−1Ke−jωt dt = 2K sinc(ω)
H(jω) = F (jω) − G(jω) = 2K(4 sinc(2ω) − sinc(ω))
5
F (jω) =∫ −1
−2e−jωt dt +
∫ 1
−1e−jωt dt +
∫ 2
1−e−jωt dt
=1jω
[2(ejω − e−jω) − (e2jω − e−2jω)
]= 4 sinc(ω) − 2 sinc(2ω)
6
F (jω) =12j
∫ πa
− πa
(ejat − e−jat)e−jωt dt
f(a) =12j
∫ πa
− πa
ejate−jωt dt =12j
∫ πa
− πa
ej(a−ω)t dt
=sinω π
a
j(a − ω)
F (jω) = f(a) + f(−a) =2jω
ω2 − a2 sinωπ
a
7
F (jω) =∫ ∞
0e−at. sinω0t.e
−jωt dt
= f(ω0) − f(−ω0)
where f(ω0) =12j
∫ ∞
0e(−a+j(ω0−ω)t) dt
=12j
(1
a − j(ω0 − ω)
)=
12j
(1
(a + jω) − jω0
)
∴ F (jω) =ω0
(a + jω)2 + ω20
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8
Fc(x) =14
∫ a
0(ejt + e−jt)(ejxt + e−jxt) dt
define g(x, b) =∫ a
0ej(b+x)t dt
=1
j(b + x)[ej(b+x)a − 1]
Fc(x) =14[g(x, 1) + g(x,−1) + g(−x, 1) + g(−x,−1)]
=12
[sin(1 + x)a
1 + x+
sin(1 − x)a1 − x
]
9 Consider F (x) =∫ a
0 1.ejxt dt
=−j
x(cos ax + j sin ax − 1)
Fc(x) = Re F (x) =sin ax
x
Fs(x) = Im F (x) =1 − cos ax
x
10 Consider F (x) =∫∞0 e−atejxt dt
=a + jx
a2 + x2
Fc(x) = Re F (x) =a
a2 + x2
Fs(x) = Im F (x) =x
a2 + x2
Exercises 5.3.6
11 Obvious
12 (jω)2Y (jω) + 3jωY (jω) + Y (jω) = U(jω)
Y (jω) =1
(1 − ω2) + 3jωU(jω)
H(jω) =1
(1 − ω2) + 3jω
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13
→ sincω
2
→ (e−iω3/2 + eiω3/2
)sinc
ω
2=
2ω
(sin(2ω) − sin(ω))= 4 sinc(2ω) − 2 sinc(ω)
14
F (jω) =∫ T
2
− T2
cos(ω0t)e−iωt dt
=1
ω0 − ωsin(ω0 − ω)
T
2+
1ω0 + ω
sin(ω0 + ω)T
2ω �= ±ω0
=T
2
[sin(ω0 − ω)T
2
(ω0 − ω)T2
+sin(ω0 + ω)T
2
(ω0 + ω)T2
]
Evaluating at ω = ±ω0 ⇒
F (jω) =T
2
[sinc(ω0 − ω)
T
2+ sinc(ω0 + ω)
T
2
]
15
F (jω) =∫ T
0cos ω0t.e
−jωt dt
=12[f(ω0) + f(−ω0)]
where f(ω0) =∫ T
0ej(ω0−ω)t dt
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=1
j(ω0 − ω)[ej(ω0−ω)T − 1] ω �= ω0
F (jω) =12
[1
j(ω0 − ω)(ej(ω0−ω)T − 1)
− 1j(ω0 − ω)
(e−j(ω0+ω)T − 1)]
= e−jωT/2[ejω0T/2
ω0 − ωsin(ω0 − ω)
T
2
+e−jω0T/2
ω0 + ωsin(ω0 + ω)
T
2
]ω �= ±ω0
Checking at ω = ±ω0 gives
F (jω) =T
2e−jωT/2
[ejω0T/2 sinc(ω0 − ω)
T
2+ e−jω0T/2 sinc(ω0 + ω)
T
2
]
16
F (jω) =∫ 1
−1sin 2t.e−jωt dt
=12j
∫ 1
−1e−j(ω−2)t − e−j(ω+2)t dt
f(a) =∫ 1
−1e−j(ω−a)t dt = 2 sinc(ω − a)
F (jω) =12j
f(a) − 12j
f(−a), a = 2
= j[sinc(ω + 2) − sinc(ω − 2)]
Exercises 5.4.3
17
I H(s) =1
s2 + 3s + 2h(t) = (e−t − e−2t)ξ(t)
H(jω) =∫ ∞
0(e−t − e−2t)e−jωt dt =
11 + jω
− 12 + jω
=1
2 − ω2 + 3jωas required.
II H(s) =s + 2
s2 + s + 1h(t) = e−1/2t
(cos
√3
2t +
√3 sin
√3
2t
)ξ(t)
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Consider G(ω0) =∫ ∞
0e−(1/2tjω−jω0)t dt
=1
12 + j(ω − ω0)
H(jω) =12G(ω0) +
12G(−ω0) +
√3
2j(G(ω0) − G(−ω0)), ω0 =
√3
2
So H(jω) =2 + 4jω
4 + 4jω − 4ω2 +6
4 + 4jω − 4ω2
=2 + jω
1 − ω2 + jω
18
P (jω) = 2AT sinc ωT
So F (jω) = (e−jωτ + eiωτ )P (jω)= 4AT cos ωτ sinc ωT
19 G(s′) =(s′)2
(s′)2 +√
2s′ + 1G(jω) =
−ω2
1 − ω2 +√
2jω
=1
1ω2 − 1 +
√2 j
ω
Thus | G(jω) |→ 0 as ω → 0and | G(jω) |→ 1 as ω → ∞High-pass filter.
20 g(t) = e−a|t| −→ G(jω) =2a
a2 + ω2
f(jt) =12G(jt) −→ πg(−ω) = πe−a|ω|
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21 F{f(t) cos ω0t} =12F (j(ω − ω0)) +
12F (j(ω + ω0))
F (jω) = 2T sinc ωT
∴ F{PT (t) cos ω0t}= T
[sinc(ω − ω0)T + sinc(ω + ω0)T
]
Exercises 5.5.322
12π
∫ ∞
−∞πδ(ω − ω0)ejωtdω +
12π
∫ ∞
−∞πδ(ω + ω0)ejωtdω
=12(ejω0t + e−jω0t)
= cos ω0t
23F{e±jω0t} = 2πδ(ω ∓ ω0)
∴ F{sinω0t} =12j
{2πδ(ω − ω0) − 2πδ(ω + ω0)}= jπ[δ(ω + ω0) − δ(ω − ω0)]
12π
∫ ∞
−∞jπ[δ(ω + ω0) − δ(ω − ω0)]ejωtdω
=j
2[e−jω0t − e+jω0t] = sinω0t
24 G(jω) =∞∫
−∞g(t)e−jωt dt; G(jt) =
∫∞−∞ g(ω)e−jωtdω
So∫ ∞
−∞f(t)G(jt) dt
=∫ ∞
−∞f(t)
(∫ ∞
−∞g(ω)e−jωtdω
)dt
=∫ ∞
−∞g(ω)
(∫ ∞
−∞f(t)e−jωt dt
)dω
=∫ ∞
−∞g(ω)F (jω)dω =
∫ ∞
−∞g(t)F (jt) dt
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25 Write result 24 as∫ ∞
−∞f(ω)F{g(t)}dω =
∫ ∞
−∞F{f(t)}g(ω)dω
so∫ ∞
−∞f(ω)F{G(jt)}dω =
∫ ∞
−∞F{f(t)}G(jω)dω
Nowg(t) → G(jω)
G(jt) → 2πg(−ω)G(−jt) → 2πg(ω)
symmetry
Thus∫ ∞
−∞f(ω).2πg(ω)dω =
∫ ∞
−∞F (jω)G(−jω)dω
or∫ ∞
−∞f(t)g(t) dt =
12π
∫ ∞
−∞F (jω)G(−jω)dω
26 F{H(t) sinω0t}
=12π
∫ ∞
−∞πj[δ(ω − u + ω0) − δ(ω − u − ω0)
][πδ(u) +
1ju
]du
=j
2[πδ(ω + ω0) − πδ(ω − ω0)
]+
12
[1
ω + ω0− 1
ω − ω0
]
=πj
2[δ(ω + ω0) − δ(ω − ω0)
]− ω0
ω2 − ω20
27
an =A
T
∫ d/2
−d/2e−nω0t dt =
Ad
Tsinc
nω0d
2, ω0 = 2π/T
f(t) =Ad
T
∞∑n=−∞
sincnω0d
2enω0t,
F (ω) =2πAd
T
∞∑n=−∞
sincnω0d
2δ(ω − nω0)
Exercises 5.6.6
28
T = 1, N = 4, ∆ω = 2π/(4 × 1) =π
2
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G0 =3∑
n=0
gne− ×n×0×π/2 = 2
G1 =3∑
n=0
gne− ×n×1×π/2 = 0
G2 =3∑
n=0
gne− ×n×2×π/2 = 2
G3 =3∑
n=0
gne− ×n×3×π/2 = 0
G = {2, 0, 2, 0}
29
N = 4, Wn = e− nπ/2
g′n =
1 0 1 00 1 0 11 0 −1 00 1 0 −1
1010
=
2000
G′ =
G00G10G01G11
=
1 1 0 01 −1 0 01 0 1 −0 0 1
2000
=
2200
Bit reversal gives
G =
2020
30 Computer experiment.
31 Follows by direct substitution.
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Review exercises 5.9
1
FS(x) =∫ 1
0t sinxt dt +
∫ 2
1sinxt dt =
sinx
x2 − cos 2x
x
2
f(t) = −π
2H(−t − 2) + (H(t + 2) − H(t − 2))
πt
4+
π
2H(t − 2)
F{H(t)} =1
ω+ πδ(ω)
F{H(t − 2)} = e−2jω[
1jω
+ πδ(ω)]
F{H(−t − 2)} = e2jω[−1
jω+ πδ(−ω)
]= e2jω
[−1jω
+ πδ(ω)]
F{f(t)} = F{−π
2H(−t − 2)} +
π
4
∫ 2
−2te−jωt dt + F
{π
2H(t − 2)
}
=−πjω
sinc 2ω
3
F {H(t + T/2) − H(t − T/2)} = T sincωT
2F {cos ω0t} = π [δ(ω + ω0) + δ(ω − ω0)]
Using convolution
F {f(t)} =π
2π
∫ ∞
−∞T sinc
T
2(ω − u) (δ(u + ω0) + δ(u − ω0))du
=T
2
[sinc(ω − ω0)
T
2+ sinc(ω + ω0)
T
2
]
4
F {cos ω0tH(t)} =12π
[πδ(ω − ω0) + πδ(ω + ω0)] ∗[πδ(ω) +
1jω
]
=12π
∫ ∞
−∞{πδ(ω − u − ω0) + πδ(ω − u + ω0)}
[πδ(u) +
1ju
]du
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=π
2[δ(ω − ω0) + δ(ω + ω0)] +
jωω2
0 − ω2
5
F{f(t) cos ωct cos ωct}
=F (jω + jωc) + F (jω − jωc)
2∗ π [δ(ω − ωc) + δ(ω + ωc)]
=14
∫ ∞
−∞[F (j(u + ωc)) + F (j(u − ωc))]×
[δ(ω − u − ωc) + δ(ω − u + ωc)] du
=12F (jω) +
14
[F (jω + 2jωc) + F (jω − 2jωc)]
Or write as
f(t)12(1 + cos 2ωct)
etc.
6
H(t + 1) − H(t − 1) ↔ 2 sinc ω
By symmetry
2 sinc t ↔ 2π(H(−ω + 1) − H(−ω − 1)) = 2π(H(ω + 1) − H(ω − 1))
7(a) Simple poles at s = a and s = b . Residue at s = a is eat/(a − b) , at s = b
it is ebt/(b − a) , thus
f(t) =1
a − b
(eat − ebt
)H(t)
7(b) Double pole at s = 2, residue is
lims→2
dds
((s − 2)2
est
(s − 2)2
)= te2t
So f(t) = te2tH(t)
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7(c) Simple pole at s = 1, residue e−t , double pole at s = 0, residue
lims→0
dds
(est
s + 1
)= (t − 1)H(t)
Thus f(t) = (t − 1 + e−t)H(t)
8(a)
y(t) =∫ ∞
−∞h(t − τ)u(τ) dτ
Thus− sinω0t =
∫ ∞
−∞h(t − τ) cos ω0τdτ = f(t), say
If u(τ) = cos ω0(τ + π/4)
y(t) =∫ ∞
−∞h(t − τ) cos ω0(τ + π/4) dτ
=∫ ∞
−∞h(t − (τ − π/4)) cos ω0τ dτ = f(t + π/4)
= − sinω0(t + π/4)
8(b) Since sinω0t = cos ω0(t − π/2ω0)
y(t) =∫ ∞
−∞h(t − τ) sinω0t dτ
=∫ ∞
−∞h(t − τ) cos ω0(τ − π/2ω0) dτ
=∫ ∞
−∞h(t − (τ + π/2ω0)) cos ω0τ dτ
= f(t − π/2ω0) = − sin(ω0t − π/2) = cos ω0t
8(c)
ejω0t = cos ω0t + j sinω0t
This is transformed from above to
− sinω0t + j cos ω0t = j ejω0t
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8(d) Proceed as above using
e−jω0t = cos ω0t − j sinω0t
9
F(sgn(t)) = F(f(t)) = F (jω) =2jω
, obvious
Symmetry,
F (jt) =2jt
↔ 2/πf(−ω) = 2πsgn(−ω)
That is1jt
↔ −πsgn(ω)
or
−(
1πt
)↔ jsgn(ω)
10
g(t) = − 1πt
∗ f(t) = − 1π
∫ ∞
−∞
f(τ)t − τ
dτ =1π
∫ ∞
−∞
f(τ)τ − t
dτ = FHi(t)
so
g(x) =1π
∫ ∞
−∞
f(t)t − x
dt = FHi(x)
So from Exercise 9
FHi(jω) = jsgn(ω) × F (jω)
so
|FHi(jω)| = |jsgn(ω)| |F (jω)| = |F (jω)|and
arg(FHi(jω)) = arg(F (jω)) + π/2, ω ≥ 0
Similarly
arg(FHi(jω)) = arg(F (jω)) − π/2, ω < 0
11 First part, elementary algebra.
FHi(x) =1π
∫ ∞
−∞
t
(t2 + a2)(t − x)dt
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=1π
1x2 + a2
∫ ∞
−∞
[a2
t2 + a2 +t
t − x− xt
t2 + a2
]dt
=a
x2 + a2
12(a)
H{f(t)} =1π
∫ ∞
−∞
f(t)t − x
dt = FHi(x)
H{f(a + t)} =1π
∫ ∞
−∞
f(a + t)t − x
dt
=1π
∫ ∞
−∞
f(t)t − (a + x)
dt = FHi(a + x)
12(b)
H{f(at)} =1π
∫ ∞
−∞
f(at)t − x
dt
=1π
∫ ∞
−∞
f(t)t − ax
dt = FHi(ax), a > 0
12(c)
H{f(−at)} =1π
∫ ∞
−∞
f(−at)t − x
dt
= − 1π
∫ ∞
−∞
f(t)t + ax
dt = −FHi(−ax), a > 0
12(d)
H{
df
dt
}=
1π
∫ ∞
−∞
f ′(t)t − x
dt
=1π
[f(t)t − x
∣∣∣∣∞
−∞+∫ ∞
−∞
f(t)(t − x)2
dt
]
Provided lim|t|→∞
f(t)/t = 0 then
H{
df
dt
}=
1π
∫ ∞
−∞
f(t)(t − x)2
dt =1π
ddx
∫ ∞
−∞
f(t)t − x
dt
=ddx
FHi(x)
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12(e)x
π
∫ ∞
−∞
f(t)t − x
dt +1π
∫ ∞
−∞f(t) dt =
1π
∫ ∞
−∞
tf(t)t − x
dt
= H{tf(t)}
13 From Exercise 10
FHi(t) = − 1πt
∗ f(t)
So from Exercise 9,
F{FHi(t)} = jsgn (ω) × F( ω)
so
F(jω) = −jsgn (ω) × F{FHi(t)}
Thus
f(t) =∫ ∞
−∞
1π(t − τ)
FHi(τ)dτ = − 1π
∫ ∞
−∞
1(x − τ)
FHi(x)dx
14
fa(t) = f(t) − jFHi(t)
F{fa(t)} = F (jω) − j(jsgn (ω))F (jω) = F (jω) + sgn (ω)F (jω)
={
2F (jω), ω > 00, ω < 0
15
F{H(t)} =1jω
+ πδ(ω) = F (jw)
Symmetry
F ( t) =1jt
+ πδ(t) ↔ 2πH(−ω) = 2π[1 − H(ω)]
= 2π[Fδ(t) − H(ω)]
or
H(ω) ↔ j2πt
+12δ(t)
Thus
F−1{H(ω)} =j
2πt+
12δ(t)
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Thenf(t) = 2
[12δ(t) +
j2πt
]∗ f(t) = f(t) − j
(− 1
πt
)∗ f(t)
= f(t) − jFHi(t)
When f(t) = cos ω0t, ω0 > 0, then
F (jω) = π[δ(ω − ω0) + δ(ω + ω0)]
soF{f(t)} = 2πδ(ω − ω0)
whencef(t) = f(t) − jFHi(t) = ejω0t = cos ω0t + j sinω0t
and soFHi(t) = − sinω0t
When g(t) = sinω0t, ω0 > 0
G(jω) = jπ[δ(ω + ω0) − δ(ω − ω0)]
and thusg(t) = −jejω0t = −j(cos ω0t + j sinω0t)
soH{sinω0t} = cos ω0t
16 If h(t) = 0, t < 0, then when t < 0
he(t) =12h(−t), and ho(t) = −1
2h(−t)
i.e. ho(t) = −he(t)
When t > 0 thenhe(t) =
12h(t), and ho(t) =
12h(t)
i.e. ho(t) = he(t)
That isho(t) = sgn (t)he(t) ∀t
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Thush(t) = he(t) + sgn (t)he(t)
When h(t) = sin t H(t)
he(t) =
12
sin t, t > 0
−12
sin t, t < 0
and sincesgn (t) he(t) =
12
sin t ∀t
the result is comfirmed.Then taking the FT of the result,
H(jω) = He(jω) + F {sgn (t)he(t)
}
= He(jω) +12π
(2jω
∗ He(jω))
= He(jω) + jH {He(jω)
}When
H(jω) =∫ ∞
−∞e−ate−jwt dt =
a
a2 + ω2 − ω
a2 + ω2
thenH{
a
a2 + ω2
}= − ω
a2 + ω2
orH{
a
a2 + t2
}= − x
a2 + x2
Finally
H{
at
a2 + t2
}= −x
x
a2 + x2 +1π
∫ ∞
−∞
a
a2 + t2dt =
a2
a2 + x2
SoH{
t
a2 + t2
}=
a
a2 + x2
17(a)
FH(s) =∫ ∞
0e−at(cos 2πst + sin 2πst) dt =
a + 2πs
a2 + 4π2s2
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17(b)
FH(s) =∫ T
−T
(cos 2πst + sin 2πst) dt =1πs
sin 2πst
18
E(s) =∫ ∞
−∞f(t) cos 2πst dt O(s) =
∫ ∞
−∞f(t) sin 2πst dt
E(s) − O(s) =∫ ∞
−∞f(t)e−j2πst dt = F (js)
From 17(a)
FH(s) =1 + πs
2 + 2π2s2
whenceE(s) =
12 + 2π2s2 , O(s) =
πs
2 + 2π2s2
soF ( s) =
1 − jπs
2 + 2π2s2
agreeing with the direct calculation
F (js) =∫ ∞
0e−2te−j2πst dt =
1 − jπs
2 + 2π2s2
19
H{f(t − T )} =∫ ∞
−∞f(t − T ) cas 2πst dt
=∫ ∞
−∞f(τ) [cos 2πsτ(cos 2πsT + sin 2πsT )+
sin 2πsτ(cos 2πsT − sin 2πsT )] dt
= cos 2πsTFH(s) + sin 2πsTFH(−s)
20 The Hartley transform follows at once since
FH(s) = �{F (js)} − {F (js)} =12δ(s) +
1sπ
From time shifting
FH(s) = sinπs
[12δ(−s) − 1
sπ
]+ cos πs
[12δ(s) +
1sπ
]
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Glyn James: Advanced Modern Engineering Mathematics, Third edition 285
=12δ(s) +
cos πs − sinπs
πs
21
H{δ(t)} =∫ ∞
−∞δ(t) cas 2πst dt = 1
From Exercise 18 it follows that the inversion integral for the Hartley transform is
f(t) =∫ ∞
−∞FH(s) cas 2πstds
and so the symmetry property is simply
f(t) ↔ FH(s) =⇒ FH(t) ↔ f(s)
Thus
H{1} = δ(s)
At once
H{δ(t − t0)}∫ ∞
−∞δ(t − t0) cas 2πst dt = cas 2πst0
By symmetry
H{cas 2πs0t} = δ(s − s0)
2212FH(s − s0) +
12FH(s + s0)
=12
∫ ∞
−∞f(t) {cos 2π(s − s0)t + sin 2π(s − s0)t
+ cos 2π(s + s0)t + sin 2π(s + s0)t} dt
=∫ ∞
−∞f(t) cos 2πs0t [cos 2πst + sin 2πst] dt
= H{f(t) cos 2πs0t}
From Exercise 21, setting f(t) = 1
H{cos 2πs0t} =12(δ(s − s0) + δ(s + s0))
c©Pearson Education Limited 2004
286 Glyn James: Advanced Modern Engineering Mathematics, Third edition
alsoH{sin 2πs0t} = H{cas 2πs0t} − H{cos 2πs0t}
= δ(s − s0) − 12(δ(s − s0) + δ(s + s0)) =
12(δ(s − s0) − δ(s + s0))
23 ∫ t
−∞(1 + τ2)−1 dτ = tan−1 t +
π
2
Thus
F{tan−1 t} = F{∫ t
−∞(1 + τ2)−1 dτ
}− F
{π
2
}
= F{∫ ∞
−∞(1 + τ2)−1H(t − τ)dτ
}− F
{π
2
}
= F{
11 + t2
∗ H(t)}
− F{π
2
}
= F{
11 + t2
}×{
1 ω
+ πδ(ω)}
− π
2× 2πδ(ω)
But from Exercise 1F{
e−|t|}
=2
1 + ω2
and so by symmetry
F{
11 + t2
}= πe−|ω|
whenceF {
tan−1 t}
= πe−|ω| ×{
1jω
+ πδ(ω)}
− π
2× 2πδ(ω)
and so
F {tan−1 t
}=
πe−|ω|
jω
2412
[1 + cos ω0t] ↔ 12
[2πδ(ω) + πδ(ω − ω0) + πδ(ω + ω0)]
andH(t + T/2) − H(t − T/2) ↔ 2T sinc ω
soF {x(t)} =
∫ ∞
−∞2T sinc (ω − u)
c©Pearson Education Limited 2004
Glyn James: Advanced Modern Engineering Mathematics, Third edition 287
×[πδ(u) +
12
(δ(ω − ω0) + δ(u + ω0))]
du
= T
[sinc ω +
12
sinc (ω − ω0) +12
sinc (ω + ω0)]
25
H(ν) =14
3∑r=0
f(r) cas2πνr
4
H(0) =14
[f(0) + f(1) + f(2) + f(3)]
H(1) =14
[f(0) + f(1) − f(2) − f(3)]
H(0) =14
[f(0) − f(1) + f(2) − f(3)]
H(0) =14
[f(0) − f(1) − f(2) + f(3)]
so
T =14
1 1 1 11 1 −1 −11 −1 1 −11 −1 −1 1
By elementary calculation T2 = 1/4T and if T−1 exists, T−1 = 4T . SinceT−1T = I , it does. Then
T−1H =
1 1 1 11 1 −1 −11 −1 1 −11 −1 −1 1
H(0)H(1)H(2)H(3)
=
f(0)f(1)f(2)f(3)
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