Straight Line Question 330

Question: The equations of two lines through $ (0,\ a) $ which are at distance ?a? from the point $ (2a,\ 2a) $ are [Dhanbad Engg. 1972]

Options:

A) $ y-a=0 $ and $ 4x-3y-3a=0 $

B) $ y-a=0 $ and $ 3x-4y+3a=0 $

C) $ y-a=0 $ and $ 4x-3y+3a=0 $

D)None of these

Show Answer

Answer:

Correct Answer: C

Solution:

  • Equation of any line through $ (0,a) $ is $ y-a=m(x-0) $ or $ mx-y+a=0 $?..(i) If the length of perpendicular from (2a, 2a) to the line (i) is ?a?, then $ a=\pm \frac{m(2a)-2a+a}{\sqrt{m^{2}+1}}\Rightarrow m=0,\frac{4}{3} $ . Hence the required equations of lines are $ y-a=0 $ , $ 4x-3y+3a=0 $ .