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


   



Question 1040743: Find the equation of the circle when 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=-32
y=-8
(8,-8)
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=24
x=4
So,
3%284%29%2B4y=-8
12%2B4y=-8
4y=-20
y=-5
(4,-5)
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,-8):
8%5E2%2B%28-8%29%5E2%2B8D-4E%2BF=0
64%2B64%2B8D-8E%2BF=0
4.8D-8E%2BF=-128
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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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(4,-5):
%284%29%5E2%2B%28-5%29%5E2%2B4D-5E%2BF=0
16%2B25%2B4D-5E%2BF=0
6.4D-5E%2BF=-41
Subtracting eq. 5 from eq. 4,
8D-8E%2BF-8D%2B2E-F=-128%2B68
-6E=-60
E=10
Substituting into eq. 4,
8D-8%2810%29%2BF=-128
7.8D%2BF=-48
Substituting into eq. 6,
4D-5%2810%29%2BF=-41
8.4D%2BF=9
Now subtracting eq. 8 from eq. 7,
8D%2BF-4D-F=-48-9
4D=-57
D=-57%2F4
Substituting into eq. 8,
4%28-57%2F4%29%2BF=9
-57%2BF=9
F=66
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x%5E2%2By%5E2-%2857%2F4%29x%2B10y%2B66=0
You can complete the square to get into center-radius form,
%28x%5E2-%2857%2F4%29x%29%2B%28y%5E2%2B10y%29%2B66=0

%28x-57%2F8%29%5E2%2B%28y%2B5%29%5E2=3249%2F64%2B1600%2F64-4224%2F64
%28x-57%2F8%29%5E2%2B%28y%2B5%29%5E2=625%2F64
%28x-57%2F8%29%5E2%2B%28y%2B5%29%5E2=%2825%2F8%29%5E2
Center : (57%2F8,-5)
Radius : 25%2F8
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