To find the center and radius of the circle given the equation \((x-7) + (y-9) = 81\), we need to rewrite the equation in the standard form of a circle, which is:
\[ (x-h)^2 + (y-k)^2 = r^2 \]
where \((h, k)\) is the center of the circle and \(r\) is the radius.
Given your equation \((x-7) + (y-9) = 81\), it looks like the equation is actually incomplete for a circle equation. The format suggests a misunderstanding or typo, but typically for a circle you would have:
\[ (x-7)^2 + (y-9)^2 = 81 \]
From this form, we can identify:
- The center \((h, k) = (7, 9)\)
- The radius \(r\) where \(r^2 = 81\), so \(r = \sqrt{81} = 9\)
Thus, the center of the circle is \((7, 9)\) and the radius is \(9\).
The correct answer is:
b. center (7, 9); r = 9.