ATLAS Geometry Circles. Practice it free.

The endpoints share the same $x$-coordinate, so the diameter is vertical with length $|9 - (-5)| = 14\textsf{.}$ The radius is half the diameter, so $r = \dfrac{14}{2} = 7\textsf{.}$

Circle A has center $(0, 6)$ and radius $8$. Shifting down $6$ moves the center to the origin, so Circle B is $x^2 + y^2 = 64$.

The radius is the distance from $(0, 0)$ to $(6, 8)\textsf{:}$ $\sqrt{6^2 + 8^2} = \sqrt{100} = 10$ units. Standard form is $(x - h)^2 + (y - k)^2 = r^2\textsf{,}$ so $x^2 + y^2 = 10^2 = 100\textsf{.}$

Area $= \dfrac{1}{2} \times 10 \times 12 = 60$.

$L = \dfrac{90}{360} \times 2 \pi r = \dfrac{1}{4} \times 2 \times 3 \times 4 = 6$.

The endpoints share the same $y$-coordinate, so the diameter is horizontal with length $|18 - 2| = 16\textsf{.}$ The radius is half the diameter, so $r = \dfrac{16}{2} = 8\textsf{.}$

Circle A has center $(6, 0)$ and radius $9$. Shifting left $6$ moves the center to the origin, so Circle B is $x^2 + y^2 = 81$.

The right side is $r^{2} = 16\textsf{,}$ so the radius measures $4$ units.