TEXAS A&M UNIVERSITY DEPARTMENT OF MATHEMATICS MATH 308-200

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TEXAS A&M UNIVERSITY
DEPARTMENT OF MATHEMATICS
MATH 308-200
Exam 2 version A, 31 Oct 2014
On my honor, as an Aggie, I have neither given nor received unauthorized aid on this work.
Name (print):
In all questions no analytical work =⇒ no points!
1.
Solve the initial value problem
y 00 − y 0 − 6y = e3t ,
using the method of your choice.
y(0) = 1, y 0 (0) = 0,
2.
Find the general solution to
y 00 + 2y 0 + y = t−2 e−t .
3.
A series circuit has a capacitor of C = 0.25 × 10−6 F, a resistor of R = 5 × 103 Ω, and
an inductor of L = 1H. The initial charge on the capacitor is zero. A 12-volt battery
is connected to the circuit and the circuit is closed at t = 0. What’s the charge on the
capacitor after a long time? Give a quick physics explanation and a full proof using the
solution of the differential equation
LQ00 + RQ0 +
1
Q = E(t).
C
4.
Prove that the Laplace transform of the function

sin(t), 0 < t < π,
g(t) =
0,
t≥π
is equal to
1
1 + e−πs .
+1
You may do it using the definition of Laplace transform or by expressing g(t) in terms of
the Heaviside function u(t) and using the formulas. Bonus (+2pnts): Do it using both
methods.
Do not attempt to fudge your answer!
G(s) =
s2
5.
Solve the initial value problem
y 00 + ω 2 y = g(t),
ω > 1, y(0) = 0, y 0 (0) = 0,
where g(t) is given in question 4. For which values of ω > 1 is the solution identically zero
when t > π.
Points:
/25
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