Straight Line Question 71

Question: In what direction a line be drawn through the point (1, 2) so that its points of intersection with the line $ x+y=4 $ is at a distance $ \frac{\sqrt{6}}{3} $ from the given point [IIT 1966; MNR 1987]

Options:

A) $ 30^{o} $

B) $ 45^{o} $

C) $ 60^{o} $

D) $ 75^{o} $

Show Answer

Answer:

Correct Answer: D

Solution:

  • Let the required line through the point (1,2) be inclined at an angle $ \theta $ to the axis of x. Then its equation is $ \frac{x-1}{\cos \theta }=\frac{y-2}{\sin \theta }=r $…..(i) where r is distance of any point (x, y) on the line from the point (1, 2). The coordinates of any point on the line (i) are $ (1+r\cos \theta ,2+r\sin \theta ) $ . If this point is at a distance $ \frac{\sqrt{6}}{3} $ form (1, 2), then $ r=\frac{\sqrt{6}}{3}. $ Therefore, the point is $ ( 1+\frac{\sqrt{6}}{3}\cos \theta ,\text{ }2+\frac{\sqrt{6}}{3}\sin \theta ) $ . But this point lies on the line $ x+y=4 $ .
    Þ $ \frac{\sqrt{6}}{3}(\cos \theta +\sin \theta )=1 $ or $ \sin \theta +\cos \theta =\frac{3}{\sqrt{6}} $
    Þ $ \frac{1}{\sqrt{2}}\sin \theta +\frac{1}{\sqrt{2}}\cos \theta =\frac{\sqrt{3}}{2} $ , {Dividing both sides by $ \sqrt{2} $ }
    Þ $ \sin (\theta +45^{o})=\sin 60^{o} $ or sin $ 120^{o} $
    Þ $ \theta =15^{o} $ or $ 75^{o} $ .



sathee Ask SATHEE

Welcome to SATHEE !
Select from 'Menu' to explore our services, or ask SATHEE to get started. Let's embark on this journey of growth together! 🌐📚🚀🎓

I'm relatively new and can sometimes make mistakes.
If you notice any error, such as an incorrect solution, please use the thumbs down icon to aid my learning.
To begin your journey now, click on

Please select your preferred language
कृपया अपनी पसंदीदा भाषा चुनें