What do you mean? just the number 80?
Answer:
Explanation:
We must write this equation in the form
(
x
−
a
)
2
+
(
y
−
b
)
2
=
r
2
Where
(
a
,
b
)
are the co ordinates of the center of the circle and the radius is
r
.
So the equation is
x
2
+
y
2
−
10
x
+
6
y
+
18
=
0
Complete the squares so add 25 on both sides of the equation
x
2
+
y
2
−
10
x
+
25
+
6
y
+
18
=
0
+
25
=
(
x
−
5
)
2
+
y
2
+
6
y
+
18
=
0
+
25
Now add 9 on both sides
(
x
−
5
)
2
+
y
2
+
6
y
+
18
+
9
=
0
+
25
+
9
=
(
x
−
5
)
2
+
(
y
+
3
)
2
+
18
=
0
+
25
+
9
This becomes
(
x
−
5
)
2
+
(
y
+
3
)
2
=
16
So we can see that the centre is
(
5
,
−
3
)
and the radius is
√
16
or 4
