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Problem 9.3
1.1x
1
+10x
2
=120
2x
1
+17.4x
2
=174
(a) Solve it graphically.
To solve graphically we express x2 in terms of x1 for both equations, plot the two lines and see where
they intersect.
x2=@(x1) (120+1.1*x1)/10
x2 =
@(x1) (120+1.1*x1)/10
And for the second equation
>> x2a=@(x1) (174+2*x1)/17.4
x2a =
@(x1) (174+2*x1)/17.4
In order to look for a graphical solution, we need to select a range to plot the functions.
If we solved the problem only for x1 we would get values of the order of 100, and if we solved only for
x2 we would get values of the order of 10. So we could try (0,200) for x1
>> fplot (x2,[0,200]); hold on
>> fplot (x2a,[0,200])
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View Full Document Obviously the solution is further away, so we try again.
>> fplot (x2,[200,500]); hold on
>> fplot (x2a,[200,500])
0
20
40
60
80
100
120
140
160
180
200
10
15
20
25
30
35
Now we are the right range but it is too broad to tell intersection. So we zoom
>> fplot (x2,[350,450]); hold on
>> fplot (x2a,[350,450])
200
250
300
350
400
450
500
30
35
40
45
50
55
60
65
70
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View Full Document We can continue to zoom.
The exact solution is
>> A=[1.1 10;2 17.4]
A =
1.1000
10.0000
2.0000
17.4000
>> b=[120;174]; sol=A\b
sol =
404.6512
56.5116.
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This note was uploaded on 03/27/2012 for the course EGM 3344 taught by Professor Raphaelhaftka during the Spring '09 term at University of Florida.
 Spring '09
 RAPHAELHAFTKA

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