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. ` ( 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. ` ( 1 )/ ( 2 ) ( a _ 1 ^ 2 + a _ 2 ^ 2 + b _ 1 ^ 2 + b _ 2 ^2 ) `
D. `sqrt ( a _ 1 ^ 2 + b _ 1 ^ 2 - a _ 2 ^ 2 - b _ 2 ^ 2 ) `

Answer

A