Question 69

A ray of light along $$x + \sqrt{3}y = \sqrt{3}$$ gets reflected upon reaching X-axis, the equation of the reflected ray is

The incident ray is given by the straight‐line equation $$x + \sqrt{3}\,y = \sqrt{3}.$$

First we write this equation in the more familiar $$y = mx + c$$ form. We simply isolate $$y$$:

We have

$$x + \sqrt{3}\,y = \sqrt{3}.$$

Subtract $$x$$ from both sides:

$$\sqrt{3}\,y = \sqrt{3} - x.$$

Now divide every term by $$\sqrt{3}$$:

$$y = \frac{\sqrt{3} - x}{\sqrt{3}} = -\frac{1}{\sqrt{3}}\,x + 1.$$

So the slope of the incident ray is $$m_{\text{incident}} = -\dfrac{1}{\sqrt{3}}.$$ However, for reflection from the $$x$$-axis we do not need the slope directly; we simply need to apply the geometrical property of reflection in the $$x$$-axis.

A reflection in the $$x$$-axis changes every point $$(x,\,y)$$ to $$(x,\,-y)$$. In other words:

$$y \;\longrightarrow\; -y.$$ This single rule gives the equation of the image (reflected) line immediately.

Starting again with the incident equation

$$x + \sqrt{3}\,y = \sqrt{3},$$

we replace $$y$$ by $$-y$$ to obtain the reflected line:

$$x + \sqrt{3}(-y) = \sqrt{3}.$$

Simplify the product $$\sqrt{3}(-y):$$

$$x - \sqrt{3}\,y = \sqrt{3}.$$

To put this result in a slightly cleaner form, we again isolate $$y$$. First subtract $$x$$ from both sides:

$$-\sqrt{3}\,y = \sqrt{3} - x.$$

Now divide by $$-\sqrt{3}$$ (remembering that dividing by a negative flips the sign):

$$y = \frac{x - \sqrt{3}}{\sqrt{3}}.$$

Finally multiply every term by $$\sqrt{3}$$ to clear the denominator:

$$\sqrt{3}\,y = x - \sqrt{3}.$$

This is exactly one of the options provided. Comparing with the choices, we see it matches Option D.

Hence, the correct answer is Option D.

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