Answer:
r = 17, two points are possible (-15, 14) and (-15, -16)
Step-by-step 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
