Question

What is the radius of the circle whose equation is x2 + y2 = 9?
3
9
81

Answer 1

what is the formula for a circle? x^2 + y^2 = r^2 ?

Answer 2

its x^2 + y^2 =9

Answer 3

radius is 3(3^2 = 9)
just compare the equations

Answer 4

yes, that's for this circle, but what about for any ole circle out there?
Isn't it x^2 + y^2 = r^2 where r is the radius?

Answer 5

for a circle centered at the origin, yeah

Answer 6

so 9 would be the r^2; just solve that