Mathematics>Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
A circle in the xy-plane has a center at (1,-6) and a diameter of 18. Which of the following is the equation of the circle?
A.(x+1)^2+(y-6)^2=324
B.(x+1)^2+(y-6)^2=81
C.(x-1)^2+(y+6)^2=324
D.(x-1)^2+(y+6)^2=81