# Method of undetermined coefficients ```Method of undetermined coefficients
Consider the system
0 −2
x =
x + et a
1 3
0
where a is an arbitrary constant vector.
Which of the following possibilities would you choose as the most
economic xp using the method of undetermined coefficients?
A. xp = ue t
B. xp = ute t + ve t
C. xp = u(te t + e t )
D. xp = ute t
E. xp = ut 2 e t + vte t + we t
Math 215/255 (Section 921)
Systems of ODE-s
2015S T1
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Undetermined coefficients (ctd)
Consider the system in the previous example.
2
Suppose that a =
. Show that xp = ate t .
−1
1
Suppose that a =
. Show that xp cannot be of the form ute t .
1
1
Now show that for a =
1
xp =
4
−3 t
t
te +
e .
−2
0
What is the source of the disparity in the forms for xp in the two examples
above?
Math 215/255 (Section 921)
Systems of ODE-s
2015S T1
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Critical points, linearizations and stability
How many critical points does the following system have?
x 0 = (2 + x)(y − x),
y 0 = (4 − x)(y + x).
A. 0
B. 1
C. 2
D. 3
E. 4
Find the linearizations of each of the critical points, and use it to identify
the nature of the critical points.
Math 215/255 (Section 921)
Systems of ODE-s
2015S T1
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```