The equation of the circle described on the common chord of the circle...
Solution:
Given two circles are x^2 + y^2 - 8x - y -15 = 0 and x^2 + y^2 - 4x - 4y - 42 = 0.
Let the equation of the common chord of the given circles be ax + by + c = 0.
The equation of the circle with this line as diameter is given by
(x - h)^2 + (y - k)^2 = r^2, where
(h, k) = (-a/2, -b/2) is the midpoint of the chord,
r = (1/2) * √(a^2 + b^2) is the radius of the circle.
Now, let's find the equation of the common chord of the given circles.
Equation of the first circle: x^2 + y^2 - 8x - y - 15 = 0
Equation of the second circle: x^2 + y^2 - 4x - 4y - 42 = 0
Subtracting the second equation from the first equation, we get
-4x + 3y + 27 = 0
Therefore, the equation of the common chord is -4x + 3y + 27 = 0.
Now, we can find the equation of the circle with this line as diameter.
Midpoint of the chord: (h, k) = (2, -9/4)
Radius of the circle: r = (1/2) * √((-4)^2 + 3^2) = √13/2
Therefore, the equation of the circle is
(x - 2)^2 + (y + 9/4)^2 = 13/2
Simplifying the equation, we get
x^2 + y^2 - 12x - 2y + 12 = 0
Hence, the correct option is (C) x^2 + y^2 - 12x - 2y + 12 = 0.
The equation of the circle described on the common chord of the circle...