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Question
The number of common tangents to the circles x2+y2+2x+8y23=0 and x2+y24x10y+19=0 is
Options:
A .  1
B .  2
C .  3
D .  4
Answer: Option C
:
C
To find the no. of common tangents, let's find the relation betweendistance between the centers of these circles and sum of their radii -
Co-ordiantes of thecenter of first circle is (-1, - 4)
Co-ordiantes of thecenter of second circle is (2, 5)
thus the distance between them is - (32+92)
= 3(10)
Now, the sumtheir radii will be -
Radius of the first circle is - 2(10)
Radius of the secondcircle is-(10)
Sum of them will be -3(10)
Since, the distance between the centres is equal to sum of their radii
Number of common tangents will be3.

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