Gujarati
Hindi
10-1.Circle and System of Circles
normal

The value of $'c'$ for which the set, $\{(x, y) | x^2 + y^2 + 2x \le 1 \} \cap \{(x, y) | x - y + c \ge 0\}$ contains only one point in common is :

A

$(-\infty , -1] \cup [3, \infty )$

B

$\{-1, 3\}$

C

$\{-3\}$

D

$\{- 1 \}$

Solution

$x^2 + y^2 + 2x – 1 = 0;$

centre $(-1, 0)$ and rad. $=\sqrt{2}$

line $x – y + c = 0$;

$\left| {\frac{{ – 1 + c}}{{\sqrt 2 }}} \right| = \sqrt 2$

$|c – 1| = 2; c – 1 = \pm 2$

$\Rightarrow c = 3$ or $-1$

Standard 11
Mathematics

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