Straight Line Question 154

Question: If the equation of the locus of a point equidistant from the points ( $ {a _{1,}}b_1 $ ) and ( $ {a _{2,}}b_2 $ ) is ( $ {a _{1,-}}a_2 $ )x+( $ {b _{1,-}}b_2 $ ) $ y+c=0 $ then the value of c is

Options:

A) $ \frac{1}{2}(a_2^{2}+b_2^{2}-a_1^{2}-b_1^{2}) $

B) $ a_1^{2}+a_2^{2}+b_1^{2}-b_2^{2} $

C) $ \frac{1}{2}(a_1^{2}+a_2^{2}-b_1^{2}-b_2^{2}) $

D) $ \sqrt{a_1^{2}+b_2^{2}-a_2^{2}-b_2^{2}} $

Show Answer

Answer:

Correct Answer: A

Solution:

  • [a] The locus is $ {{(h-a_1)}^{2}}+{{(k-b_1)}^{2}}={{(h-a_2)}^{2}}+{{(k-b_2)}^{2}} $

$ \Rightarrow (a_1-a_2)x+(b_1-b_2)y+\frac{1}{2}(a_2^{2}+b_2^{2}-a_1^{2}-b_1^{2})=0 $

$ \Rightarrow c=\frac{1}{2}(a_2^{2}+b_2^{2}-a_1^{2}-b^2_1) $