Math 257/316, Midterm 1, Section 104
17 October 2007
Instructions. The duration of the exam is 55 minutes. Answer all questions. Calculators are not allowed.
Maximum score 100.
1. Let f (x) = x on the interval 0 < x < π.
(a) Sketch the even periodic extension of f with period 2π.
[5 marks]
(b) Expand f (x) in a Fourier cosine series.
[15 marks]
Hint: It may be useful to know that
Zπ
x cos(nx)dx =
0
½
0 if n is even
if n is odd
−2
n2
2. Apply the method of separation of variables to determine the solution to the one dimensional heat
equation with the following mixed boundary conditions:
∂u
∂t
=
BC
:
IC
:
∂2u
, 0 < x < π, t > 0
∂x2
∂u(0, t)
= 0 = u(π, t)
∂x
5
u(x, 0) = 3 cos( x)
2
[40 marks]
3. Consider the second order differential equation:
Ly = 4x2 y 00 − (x2 + x)y 0 + y = 0
(1)
(a) Classify the points x ≥ 0 (do not include the point at infinity) as ordinary points, regular singular
points, or irregular singular points.
[5 marks]
(b) Use the appropriate series expansion about the point x = 0 to determine two independent solutions
to (1). You only need to determine the first three non-zero terms in each case.
[35 marks]
1