lf the equation of the locus of a point equidistant from the points (a1,b1) and (a2,b2) is (a1−a2)x+(b1−b2)y+c=0 then the value of c is
A
12(a22+b22−a21−b21)
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B
a21−a22+b21−b22
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C
12(a21+a22+b21+b22)
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D
√a21+b21−a22−b22
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Solution
The correct option is B12(a22+b22−a21−b21) Let P(h,k) be a point which is equidistant from A(a1,b1) and B(a2,b2) i.e. PA=PB ⇒(h−a1)2+(k−b1)2=(h−a2)2+(k−b2)2 ⇒2(a1−a2)h+2(b1−b2)k+(a22−a21)+(b22−b21)=0 ⇒(a1−a2)x+(b1−b2)y+12(a22−a21)+12(b22−b21)=0 Comparing with the given equation of locus (a1−a2)x+(b1−b2)y+c=0 ⇒c=12(a22−a21+b22−b21)=0