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NDA Math Circle
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© examsnet.com
Question : 6
Total: 26
What is the radius of the circle
4
x
2
+
4
y
2
−
20
x
+
12
y
−
15
=
0
?
[NDA-I 2021]
14 units
10.5
units
7 units
3.5
units
Validate
Solution:
👈: Video Solution
Concept
Equation of circle having centre
(
h
,
k
)
and radius
r
is
(
x
−
h
)
2
+
(
y
−
k
)
2
=
r
2
Calculation:
Given equation of circle is,
4
x
2
+
4
y
2
−
20
x
+
12
y
−
15
=
0
⇒
4
x
2
−
20
x
+
25
+
4
y
2
+
12
y
+
9
−
15
−
34
=
0
⇒
(
2
x
−
5
)
2
+
(
2
y
+
3
)
2
=
49
⇒
4
(
x
−
5
2
)
2
+
4
(
y
+
3
2
)
2
=
49
⇒
(
x
−
5
2
)
2
+
(
y
+
3
2
)
2
=
(
7
2
)
2
So, the radius of the circle
=
7
2
units
=
3.5
units
© examsnet.com
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