Write the equation of the circle: center at (0,0), diameter 18

x^2+y^2=81

Step-by-step explanation:

the equation is

(x-h) ^2 + (y-k) ^2=r^2

since the center is (0,0) you don't even put it in the equation

so all you will have is the x and the y

you leave in the square (^2)

you divide the diameter by 2 to get the radius

9

then you square the radius

81