Show that the points A(1, 0), B(2, – 7), c(8, 1) and D(9, – 6) all lie on the same circle. Find the equation of this circle, its centre and radius.
Show that the points A(1, 0), B(2, – 7), c(8, 1) and D(9, – 6) all lie on the same circle. Find the equation of this circle, its centre and radius.

Answer:

 

 

 

 

The general equation of a circle: (x – h)2 + (y – k)2 = r2 …(i)

(h, k) is the centre and r is the radius.

Putting (1, 0) in (i)

(1 – h)2 + (0 – k)2 = r2

h2 + k2 + 1 – 2h = r2 ..(ii)

Putting (2, – 7) in (i)

(2 – h)2 + ( – 7 – k)2 = r2

h2 + k2 + 53 – 4h + 14k = r2

(h2 + k2 + 1 – 2h) + 52 – 2h + 14k = r2

h – 7k – 26 = 0..(iii)

Putting (8, 1)

7h + k – 32 = 0..(iv)

Solving (iii)&(iv)

h = 5 and k = – 3

Centre = (5, – 3)

Radius = 25

(9, – 6) lies on the circle, (9 – 5)2 + ( – 6 + 3)2 = 52

Hence, proved.