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Unformatted text preview: MTHSC 208 (Diﬀerential Equations)
Dr. Matthew Macauley
HW 19
Due Friday April 3rd, 2009
(1) The function −π ≤ t < π/2,
0
1
−π/2 ≤ t < π/2,
f (t) = 0
π/2 ≤ t ≤ π,
can be extended to be periodic of period 2π . Sketch the graph of the resulting function,
and compute its Fourier series.
(2) The function
f (t) = t,
for t ∈ [−π, π ]
can be extended to be periodic of period 2π . Sketch the graph of the resulting function,
and compute its Fourier series.
(3) The function
0
−π ≤ t < 0,
t
0 ≤ t ≤ π,
can be extended to be periodic of period 2π . Sketch the graph of the resulting function,
and compute its Fourier series.
f (t) = (4) Consider the 2π periodic function deﬁned by
f (t) = t2
f (t − 2kπ ), −π ≤ t < π,
−π + 2kπ ≤ t < π + 2kπ. Sketch this function and compute its Fourier series.
(5) Find the Fourier series of the function f (t) = 2 − 3 sin 4t + 5 cos 6t, and sketch the graph
of this function (use your calculator). Hint: this problem is simple – don’t do any integrals!
(6) Sketch the graph of the function f (t) = sin2 t and ﬁnd its Fourier series. Hint: Don’t do
any integrals! Instead, use a standard trig identity.
(7) Which functions from the previous exercises had only cosine terms in their Fourier series
expansion? Which functions only had sine terms? Which had both? Do you see a pattern?
Hint: compare the symmetries of the graphs of these functions to the symmetries of the
graphs of sine waves and cosine waves. ...
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 Spring '09
 Staufeneger
 Differential Equations, Equations

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