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,UNIVERSITY EXAMINATIONS
May/June 2022
APM3700
Differential Equations (Engineering)
Duration: 3 hours Marks: 100
Examiners:
First: Ms LE Greyling
Second: Mr S Blose
External: Dr JN Mwambakana
Use of a non-programmable pocket calculator is permissible.
This is a closed book examination and will be IRIS invigilated.
This online paper is the property of UNISA and may not be distributed electronically.
This examination question paper consists of 3 pages including this cover page plus
Formulae sheets (pages 4 to 8) plus
A table of integrals (pages 9 and 10) plus
A table of Laplace transforms (page 11).
Examination rules:
1. Students must upload their answer scripts in a single PDF file (answer scripts must not be password
protected or uploaded as “read only” files).
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correct answer script file has uploaded.
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their initial submission be unsatisfactory.
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resubmission will be granted.
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resubmission will be granted.
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processes. UNISA has a zero tolerance for plagiarism and/or any other forms of academic dishonesty.
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Include screenshots of your problem.
, -2- APM3700
May/June 2022
QUESTION 1
Solve the following first order differential equations:
dy
1.1 x y 2 xy (6)
dx
1.2 sin y 2xy x dx x cos y x dy 0
2 2
[Hint: First show that the equation is exact] (6)
dy ex
1.3 y , given that y (e) 0 (8)
dx x
[20]
QUESTION 2
Find the general solution of the following differential equation using the method of
d 2y dy
undetermined coefficients: 2
5 6y e3x (8)
dx dx
[8]
QUESTION 3
Find the general solution of the following differential equation using D-operator methods:
D 2
6D 9 y x 2e3 x (6)
[6]
QUESTION 4
Solve for x only by using D-operator methods in the following set of simultaneous
equations:
D 1 x 2D 7 y et 2 (10)
2 x D 3 y et 1
[10]
QUESTION 5
Determine the following:
5.1
L e 3t t 2 4 (3)
1
5.2 L1 2 (4)
s 2s 5
[7]
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, -3- APM3700
May/June 2022
QUESTION 6
d 2i di
Determine the current i in the circuit where 2
6 13i 0 if i 0 24 and i 0 4 ,
dt dt
by using Laplace transforms. (8)
[8]
QUESTION 7
Solve the given equation by using Laplace transforms:
y " 4 y 3H (t 4)
The initial values of the equation are y 0 1 and y ' 0 0 . (9)
[9]
QUESTION 8
The conditions in a certain electrical circuit are represented by the following differential
d 2i di
equation: 2 2 2i 85 sin 3t . Determine the general solution for the current, i ,
dt dt
di
in terms of t, given that for t = 0, i = 0 and 20.
dt (10)
[10]
QUESTION 9
1 1 1
If A 4 2 4 , find an eigenvector corresponding to the eigenvalue 2 .
1 1 5
Verify that 2 is an eigenvalue of A. (10)
[10]
QUESTION 10
A periodic function f(x) with period 2 is defined by:
f x 2 x, 0 x 2
Determine the Fourier expansion of the periodic function f(x). (12)
[12]
Full marks = 100
©
UNISA 2022
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