How do you find the equation of the circle, center C(4,-8), tangent to the y-axis?

1 Answer
Jan 29, 2016

Answer:

# (x - 4 )^2 + (y + 8 )^2 = 16 #

Explanation:

The equation of a circle is : # (x-a)^2 + (y - b )^2 = r^2#

(a , b ) are the coordinates of the centre and r , the radius.

The centre is given ( 4 , -8 ) . Require the radius r .

Since the y-axis is a tangent then the distance from centre

to the y-axis is 4 units. Hence r = 4 .

equation is : # (x - 4 )^2 + (y + 8 )^2 =4^2#

#(x - 4 )^2 + (y + 8 )^2 = 16#