Answer: The radius is
r
=
3
.
Explanation:
If the point
(
−
3
,
2
)
belongs to the circle
(
x
+
3
)
2
+
(
y
+
1
)
2
−
r
2
=
0
then its coordinates must verify that equation. That is, if we substitute in the equation of the circle
x
by
−
3
and
y
by
2
we must obtain a true equality. Then, it is enough to clear
r
of that equation:
(
−
3
+
3
)
2
+
(
2
+
1
)
2
−
r
2
=
0
⇒
9
−
r
2
=
0
,
then:
r
=
√
9
=
3
.
(Remember
r
is a distance, then it's always a positive number).
Step-by-step explanation:
