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UPSC CDS Math Circle Questions
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© examsnet.com
Question : 19
Total: 46
The distance between the centres of two circles having radii 9 cm and 4 cm is 13 cm. What is the length of the direct common tangent of these circles ?
[2017 CDS-II]
12 cm
11 cm
10 cm
9.5 cm
Validate
Solution:
Sum of radii of the circles
=
9
+
4
=
13
c
m
=
Distance between the centres of the circle
So, the two circles touch each other externally.
Therefore, length of the direct common tangent
=
√
(Distance between the centres
)
2
−
(
Difference between the radii
)
2
=
√
13
2
−
(
9
−
4
)
2
=
√
169
−
25
=
√
144
=
12
c
m
© examsnet.com
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