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Question 69

Locus of the image of the point (2, 3) in the line $$(2x - 3y + 4) + k(x - 2y + 3) = 0$$, k $$\in \mathbb{R}$$, is a

The given equation is $$(2x - 3y + 4) + k(x - 2y + 3) = 0$$. This represents a family of lines passing through the intersection of:

$$L_1: 2x - 3y + 4 = 0$$ and $$L_2: x - 2y + 3 = 0$$

    To find the intersection point ($$P$$), solve the two equations

    $$\implies \mathbf{y = 2}$$, $$\mathbf{x = 1}$$.

    Thus, all lines in the family pass through the fixed point $$P(1, 2)$$.

    Let $$A(2, 3)$$ be the given point and $$A'$$ be its image in any line $$L$$ from the family.

    By the definition of a reflection, the line $$L$$ is the perpendicular bisector of the segment $$AA'$$.

    Since the fixed point $$P(1, 2)$$ lies on every such line $$L$$, it must be equidistant from the point $$A$$ and its image $$A'$$.

    $$\text{Therefore, } PA = PA'$$

    $$PA = \sqrt{(2-1)^2 + (3-2)^2} = \sqrt{1^2 + 1^2} = \sqrt{2}$$

    Since $$PA' = PA = \sqrt{2}$$, the image $$A'$$ always remains at a constant distance of $$\sqrt{2}$$ from the fixed point $$P(1, 2)$$.

    The locus of a point moving at a constant distance from a fixed point is a circle, 

    with Center: $$(1, 2)$$, and Radius: $$\sqrt{2}$$

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