CircleHardBloom L3

Question

Coordinates of the centre of a circle, whose radius is 2 unit and which touches the line pair $x^{2} - y^{2} - 2x + 1 = 0$ are:

Options

A.$(4,0)$
B.$(1 + 2\sqrt{2},0)$
C.$(4,1)$
D.$(1,2\sqrt{2})$

Solution

[Key Concept: The pair $x^{2} - y^{2} - 2x + 1 = 0$ is $(x{- 1)}^{2} - y^{2} = 0$ — two lines through $(1,0)$; a radius-2 circle touching both has its centre at distance $2$ from each.]

Centre of circles which touches the lines

$$\begin{matrix} & x + y = 1\text{~}\text{and}\text{~}x - y = 1 \\ & \text{~}\text{are}\text{~}\ (1 \pm 2\sqrt{2},0)\text{~}\text{and}\text{~} \\ & \ (1, \pm 2\sqrt{2}) \end{matrix}$$

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