math 234, spring 2014 final exam keymacs.citadel.edu/wittman/234/exams/final_234_14s_key.pdf ·...
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Math 234, Spring 2014 Final Exam Key 1.) [10 points] Find the solution of the system, if it exists. Show all work.
12 321 −=++ xxx
332 31 =− xx
2223 321 =−+ xxx
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2.) [20 points] Given the following matrices.
−
−
=
243
043
121
A ,
−=
213
602B
Compute following quantities, if they exist. If the quantity is undefined, explain why.
a.) BA +
b.) AB
c.) BA
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#2 continued...
−
−
=
243
043
121
A ,
−=
213
602B
d.) BBT
e.) || A
f.) || B
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3.) [10 points] Find an explicit solution for the following first-order differential equations.
a.) ���� + 3�� = 5� − 2
b.) �� = x�sec(3�)
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4.) [10 points] Find the general solution of the second-order differential equation:
��� − 4�� + 8� = 40�� − 40�
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5.) [10 points] Find the indicated Laplace Transform.
a.) ℒ�2� + ��� cos(4�)�
b.) ℒ��� sin(3�)�
c.) ℒ�cos(6�)!(� − 4)�
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6.) [10 points] Find the indicated Inverse Laplace Transform.
a.) ℒ�" # $%�&$'""(
b.) ℒ�" # $')+
$%')(
c.) ℒ�" # *+,-
$%�.(
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7.) [10 points] Solve the initial value problem
��� − 4�� + 3� = 2/(� − 10), �(0) = 2,��(0) = 0
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8.) [10 points] A 2x2 matrix A has the eigenvalues and eigenvectors below.
3 1 −=λ ,
=
1
51vv
, 42 =λ ,
−=
1
12vv
a.) Write the general solution of the system of differential equations xAxvv
=′ .
c.) Classify the origin as an attractor, repeller, or saddle point and sketch the phase portrait.
c.) Find the specific solution �2 that satisfies the initial condition �2(0) = 3−23 4.
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9.) [10 points] Find the general solution of the system of differential equations
�2� = 35 −51 3 4 �2