Question

A circle is centered at the point (-7, -1) and passes through the point (8, 7).\

The radius of the circle is ____ units. The point (-15, ___) lies on this circle.

Answer 1

r = 17, two points are possible (-15, 14) and (-15, -16)

Explanation:

Radius is a distance between the center and any point. Use the distance formula: r = sqrt( (8-(-7))^2 + (7-(-1))^2) = 17.

Now you can use distance formula to find the possible y coordinates of the points when x = -15:

17= sqrt( (-15 - (-7))^2 + (y-(-1))^2

289 = 8^2 + (y+1)^2

225 = (y+1)^2

from here you need to split into two possibilities:

1. y+1 = 15 then y = 14

2. y+1 = -15 then y = -16