Find the equation of the circle which is circumscribed about the triangle whose vertices are A( - 2, 3), b(5, 2) and C(6, - 1). Find the centre and radius of this circle.
The general equation of a circle: (x - h)2 + (y - k)2 = r2
…(i), where (h, k) is the centre and r is the radius.
Putting A( - 2, 3), B(5, 2) and c(6, - 1) in (i) we get
h2 + k2 + 4h - 6k + 13 = r2 …(ii)
h2 + k2 - 10h - 4k + 29 = r2 …(iii)and
h2 + k2 - 12h + 2k + 37 = r2 …(iv)
subtracting (ii) from (iii) and also from (iv),
- 14h + 2k + 16 = 0 - 7h + k + 8 = 0
- 16h + 8k + 24 = 0 - 2h + k + 3 = 0
Subtracting,
5h - 5 = 0h = 1
k = - 1
Centre = (1, - 1)
Putting these values in (ii) we get, radius = = 5
Equation of the circle is
(x - 1)2 + {y - ( - 1)}2 = 52
(x - 1)2 + (y + 1)2 = 25.