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10-1.Circle and System of Circles
normal
Length of the tangent drawn from any point on the circle ${x^2} + {y^2} + 2gx + 2fy + {c_1} = 0$ to the circle ${x^2} + {y^2} + 2gx + 2fy + c = 0$ is
A
$\sqrt {{c_1} - c} $
B
$\sqrt {c - {c_1}} $
C
$\sqrt {{c_1} + c} $
D
None of these
Solution
(b) Suppose $({x_1},\;{y_1})$ be any point on first circle from which tangent is to be drawn, then
$x_1^2 + y_1^2 + 2g{x_1} + 2f{y_1} + {c_1} = 0$….$(i)$
and also length of tangent
$ = \sqrt {{S_2}} = \sqrt {x_1^2 + y_1^2 + 2g{x_1} + 2f{y_1} + c} $….$(ii)$
From $(i)$, we get $ (ii)$ as $\sqrt {c – {c_1}} $.
Standard 11
Mathematics