The standard equation of a circle with center
(
h
,
k
)
is
(
x
−
h
)
2
+
(
y
−
k
)
2
=
r
2
, with radius
r
.
When we have a circle centered at the origin, this equation turns into
x
2
+
y
2
=
r
2
Notice that our
(
h
,
k
)
goes away. We know that
r
=
8
, so we can plug this in. We get
x
2
+
y
2
=
8
2
⇒
x
2
+
y
2
=
64
Hope this helps!
