JEE Challenger
More from Straight Lines

Equation of Straight Line Inclined at Sixty Degrees

A straight line LL through the point (3,−2)(3,-2) is inclined at an angle 60∘60^\circ to the line 3x+y=1\sqrt{3}x + y = 1. If LL also intersects the xx-axis, then the equation of LL is

Options

A

y+3x+2−33=0y + \sqrt{3}x + 2 - 3\sqrt{3} = 0

B

y−3x+2+33=0y - \sqrt{3}x + 2 + 3\sqrt{3} = 0

Correct
C

3y−x+3+23=0\sqrt{3}y - x + 3 + 2\sqrt{3} = 0

D

3y+x−3+23=0\sqrt{3}y + x - 3 + 2\sqrt{3} = 0

Step-by-Step Solution

To find the equation of the straight line LL, we first determine the slope of the given line:
3x+y=1  ⟹  y=−3x+1\sqrt{3}x + y = 1 \implies y = -\sqrt{3}x + 1

The slope of this line is m1=−3m_1 = -\sqrt{3}.
Thus, its angle of inclination θ1\theta_1 with the positive direction of the xx-axis is:
tan⁡θ1=−3  ⟹  θ1=120∘\tan \theta_1 = -\sqrt{3} \implies \theta_1 = 120^\circ

The line LL is inclined at an angle of 60∘60^\circ to the given line. Therefore, the angle of inclination θ\theta of line LL can be:
θ=θ1±60∘\theta = \theta_1 \pm 60^\circ

This gives two possible inclinations for LL:

  1. θ=120∘+60∘=180∘≡0∘\theta = 120^\circ + 60^\circ = 180^\circ \equiv 0^\circ
  2. θ=120∘−60∘=60∘\theta = 120^\circ - 60^\circ = 60^\circ

Case 1: If θ=0∘\theta = 0^\circ:
The slope of line LL is m=tan⁡0∘=0m = \tan 0^\circ = 0.
The equation of the line passing through (3,−2)(3, -2) with slope 00 is:
y−(−2)=0(x−3)  ⟹  y=−2y - (-2) = 0(x - 3) \implies y = -2
This line is parallel to the xx-axis and hence does not intersect the xx-axis. Since the problem explicitly states that LL intersects the xx-axis, this case is rejected.

Case 2: If θ=60∘\theta = 60^\circ:
The slope of line LL is m=tan⁡60∘=3m = \tan 60^\circ = \sqrt{3}.
The equation of the line passing through (3,−2)(3, -2) with slope 3\sqrt{3} is:
y−(−2)=3(x−3)y - (-2) = \sqrt{3}(x - 3)
y+2=3x−33y + 2 = \sqrt{3}x - 3\sqrt{3}
y−3x+2+33=0y - \sqrt{3}x + 2 + 3\sqrt{3} = 0

This line intersects the xx-axis, satisfying all conditions.

Therefore, the correct option is (B).