SOLUTION: Find the equation of the circle if a triangle whose sides lie on the lines 3x+4y=8, 3x-4y=32 and x-8=0 inscribed the circle.

Algebra ->  Circles -> SOLUTION: Find the equation of the circle if a triangle whose sides lie on the lines 3x+4y=8, 3x-4y=32 and x-8=0 inscribed the circle.       Log On


   



Question 1040661: Find the equation of the circle if a triangle whose sides lie on the lines 3x+4y=8, 3x-4y=32 and x-8=0 inscribed the circle.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Find the intersection points.
From eq. 3,
x=8
Substituting into eq. 1,
3%288%29%2B4y=8
24%2B4y=8
4y=-16
y=-4
(8,-4)
Substituting into eq. 2,
3%288%29-4y=32
24-4y=32
-4y=8
y=-2
(8,-2)
Finally adding eq. 1 and eq. 2,
3x%2B4y%2B3x-4y=8%2B32
6x=40
x=40%2F6
x=20%2F3
So,
3%2820%2F3%29%2B4y=8
20%2B4y=8
4y=-12
y=-3
(20/3,-3)
Now you have three points on the circle, solve for the circle.
Use the general form,
x%5E2%2By%5E2%2BDx%2BEy%2BF=0
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(8,-4):
8%5E2%2B%28-4%29%5E2%2B8D-4E%2BF=0
64%2B16%2B8D-4E%2BF=0
4.8D-4E%2BF=-80
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(8,-2):
8%5E2%2B%28-2%29%5E2%2B8D-2E%2BF=0
64%2B4%2B8D-2E%2BF=0
5.8D-2E%2BF=-68
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(20/3,-3):
%2820%2F3%29%5E2%2B%28-3%29%5E2%2B%2820%2F3%29D-3E%2BF=0
400%2F9%2B9%2B%2820%2F3%29D-3E%2BF=0
400%2B81%2B60D-27E%2B9F=0
6.60D-27E%2B9F=-481
Subtracting eq. 5 from eq. 4,
8D-4E%2BF-8D%2B2E-F=-80%2B68
-2E=-12
E=-6
Substituting into eq. 4,
8D-4%286%29%2BF=-80
7.8D%2BF=56
Substituting into eq. 6,
60D-27%286%29%2B9F=-481
8.60D%2B9F=-319
Multiply eq. 7 by -9 and add to eq. 8,
-72D-9F%2B60D%2B9F=504-319
-12D=185
D=-185%2F12
and substituting into eq. 7,
8%28-185%2F12%29%2BF=-56
F=-672%2F12%2B1480%2F12
F=808%2F12
F=202%2F3
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x%5E2%2By%5E2-%28185%2F12%29x%2B6y%2B202%2F3=0
You can complete the square to get into center-radius form,
%28x%5E2-%28185%2F12%29x%29%2B%28y%5E2%2B6y%29%2B202%2F3=0

%28x-185%2F24%29%5E2%2B%28y%2B3%29%5E2=34225%2F576%2B5184%2F576-38784%2F576
%28x-185%2F24%29%5E2%2B%28y%2B3%29%5E2=625%2F576
%28x-185%2F24%29%5E2%2B%28y%2B3%29%5E2=%2825%2F24%29%5E2
Center : (185%2F24,-3)
Radius : 25%2F24
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