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Previous Year Question (PYQs)
3
A ray of light passing through the point $(1,2)$ reflects on the $X$–axis at point $A$,
and the reflected ray passes through the point $(5,3)$.
The coordinates of $A$ are:
Solution
Let $A = (x,0)$.
Slope of incident ray $= \dfrac{2 - 0}{1 - x} = \dfrac{2}{1 - x}$
Slope of reflected ray $= \dfrac{3 - 0}{5 - x} = \dfrac{3}{5 - x}$
For reflection from $X$–axis: angle of incidence = angle of reflection.
Hence, their slopes are negatives of each other:
$\dfrac{2}{1 - x} = -\dfrac{3}{5 - x}$
$\Rightarrow 2(5 - x) = -3(1 - x)$
$\Rightarrow 10 - 2x = -3 + 3x$
$\Rightarrow 5x = 13 \Rightarrow x = \dfrac{13}{5}$
Thus, $A\left(\dfrac{13}{5}, 0\right)$.
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