MHT CET · Maths · Straight Lines

The equation of a line, whose perpendicular distance from the origin is 5 units and the angle, which the perpendicular to the line from the origin makes, is \(210^{\circ}\) with positive \(\mathrm{X}\)-axis, is

A \(-x \sqrt{3}+y+10=0\)
B \(x \sqrt{3}+y-10=0\)
C \(x \sqrt{3}+y+10=0\)
D \(x \sqrt{3}-y+10=0\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(x \sqrt{3}+y+10=0\)

Step-by-step Solution

Detailed explanation

Here, \(P=5\) and \(\alpha=210^{\circ}\)
Writing the equation of straight line in normal form
\(\begin{aligned} & \Rightarrow x \cos \left(210^{\circ}\right)+y \sin 30^{\circ}=5 \\ & \Rightarrow-x \cos 30^{\circ}-y \sin 30^{\circ}=5 \\ & \Rightarrow-x \cdot \frac{\sqrt{3}}{2}-y \cdot \frac{1}{2}=5 \\ & \Rightarrow-\sqrt{3} x-y=10 \\ & \Rightarrow \sqrt{3} x+y+10=0\end{aligned}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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