First slide

Equation of line in Straight lines

Question

A light ray emerging from the point source placed at P(2,3) is reflected at a point Q on the y-axis. It then passes through the point R(5, l0). The coordinates of Q are

Moderate

A

(0,3)
B

(0,2)
C

(0, 5)
D

none of these

Solution

The point of coincidence on $the y -axis is Q (0, λ) .$
The image of P(2,3) on the $y -axis is P_{1} (- 2, 3)$
Therefore,
$Slope of P_{1} Q = Slope of P_{1} R$
$or \frac{λ - 3}{0 - (- 2)} = \frac{10 - 3}{5 - (- 2)}$
$\begin{array}{ll} or λ - 3 = 2 \\ or λ = 5 \end{array}$
Therefore, the point Q is (0, 5).

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