Straight Line Question 266

Question: The circumradius of the triangle formed by the three lines $ y+3x-5=0;y=x $ and $ 3y-x+10=0 $ is

Options:

A) $ \frac{25}{4\sqrt{2}} $

B) $ \frac{25}{3\sqrt{2}} $

C) $ \frac{25}{2\sqrt{2}} $

D) $ \frac{25}{\sqrt{2}} $

Show Answer

Answer:

Correct Answer: A

Solution:

  • [a] Two of the given lines $ y+3x-5=0 $ and $ 3y-x+10=0 $ are $ \bot $ to each other, so the triangle is right angled and it circumradius is half the hypotenuse, $ y=x $ intersects other two lines in $ ( \frac{5}{4},\frac{5}{4} ) $ and $ (-5,-5), $

$ \therefore Circumradius=\frac{1}{2}[ \sqrt{{{( -5-\frac{5}{4} )}^{2}}+{{( -5-\frac{5}{4} )}^{2}}} ] $ $ =\frac{1}{2}[ \sqrt{\frac{625}{16}+\frac{625}{16}} ]=\frac{1}{2}[ \frac{25\sqrt{2}}{4} ]=\frac{25}{4\sqrt{2}} $