Write the equation of the circle with center at (0,-1) and an area of 9pi

We can find the radius by solving this :

9pi  = pi * r^2       divide both sides by pi

9 = r^2      take the square root of both sides

3 = r

So......the equation is :

( x - 0)^2   + ( y + 1)^2   = 9    which simplifies to

x^2  + ( y + 1)^2   = 9