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10-1.Circle and System of Circles
normal
The equation of the chord of the circle ${x^2} + {y^2} = {a^2}$ having $({x_1},{y_1})$ as its mid-point is
A
$x{y_1} + y{x_1} = {a^2}$
B
${x_1} + {y_1} = a$
C
$x{x_1} + y{y_1} = x_1^2 + y_1^2$
D
$x{x_1} + y{y_1} = {a^2}$
(IIT-1983)
Solution
(c) $T = {S_1}$ is the equation of desired chord,
hence $x{x_1} + y{y_1} – {a^2} = x_1^2 + y_1^2 – {a^2}$
$\Rightarrow x{x_1} + y{y_1} = x_1^2 + y_1^2$.
Standard 11
Mathematics