A circle has a center that falls on the line y = 8/7x +2 and passes through ( 2 ,1 ) and (3 ,6 ). What is the equation of the circle?

1 Answer
Nov 6, 2016

C(70/47,174/47) radius=root2(16705/2209)
Equation of circumference is (x-70/47)^2+(y-174/47)^2=16705/2209

Explanation:

A(2,1) and B(3,6) a point C on the line y=8/7x+2 has coordinates C(x,8/7x+2).

The centre C can be found by imposing that AC=BC

root2((2-x)^2+(1-8/7x-2)^2)=root2((3-x)^2+(6-8/7x-2)^2)
By squaring boh members we get

4-4x+x^2+1+16/7x+64/49x^2=9-6x+x^2+16-64/7x+64/49x^2
that properly manipulated becomes
16/7x-4x+64/7x+6x=25-5 from which
x=70/47 and consequently
y=8/7*70/47+2=80/47+2=174/47.
These are the coordinates of the centre C
The squared radius is R^2=(2-70/47)^2+(1-174/47)^2=16705/2209