Question

Write the equation in standard form for a circle with the center (-8,7) and tangent to the x-axis

Answer 1

here, given the center = (-8,7) and its radius = 7 (because the tangen line to the x-axis). so, just put the values above to the equation of circle :
(x-h)^2 + (y-k)^2 = r^2
with (h,k) is the center and r its radius.

Answer 2

Ok. I understand about the equation but how did you know the radius was 7?