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Find the Equation of the Circle Which Circumscribes the Triangle Formed by the Lines X + Y = 2, 3x − 4y = 6 and X − Y = 0.

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Question

Find the equation of the circle which circumscribes the triangle formed by the lines

 x + y = 2, 3x − 4y = 6 and x − y = 0.

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Solution

In \[∆\]ABC:
Let AB represent the line x + y = 2.          ...(1)
Let BC represent the line 3x − 4y = 6.      ...(2)
Let CA represent the line x − y = 0.          ...(3)

Intersection point of (1) and (3) is (1, 1).
Intersection point of (1) and (2) is (2, 0).
Intersection point of (2) and (3) is (−6, −6).

The coordinates of A, B and C are (1, 1), (2, 0) and (−6, −6), respectively.
Let the equation of the circumcircle be 

\[x^2 + y^2 + 2gx + 2fy + c = 0\]

It passes through A, B and C.

∴ \[2 + 2g + 2f + c = 0\]

\[4 + 4g + c = 0\]
\[72 - 12g - 12f + c = 0\]
\[\therefore g = 2, f = 3, c = - 12\]

Hence, the required equation of the circumcircle is 

\[x^2 + y^2 + 4x + 6y - 12 = 0\]
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Advanced Concept of Circle - Standard Equation of a Circle
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Chapter 24: The circle - Exercise 24.2 [Page 32]

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R.D. Sharma Mathematics [English] Class 11
Chapter 24 The circle
Exercise 24.2 | Q 7.3 | Page 32

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