The length of the tangent from the radical centre of the three circles x2+y2+ax+by+c=0(r=1,2,3,andc>0) to one of the three circles is
A
√a1+b1+c
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B
c
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C
√c
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D
√a1a2a3+b1b2b3
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Solution
The correct option is C√c s1:x2+y2+a1x+b1y+c=0 s2:x2+y2+a2x+b2y+c=0 s3:x2+y2+a3x+b3y+c=0 So, radical axis is s1−s2=0 (a1−a2)x+(b1−b2)y=0 ---(1) and other radical axis is s1−s3=0 (a1,−a3)x+(b1,−b3)y=0 ---(2) Let (h,k) is a radical centre then L= lenght of tangent =√h2+k2+a1h+b1k+c from (1) & (2) y= 0, x= 0. (0,0) is radical centre of given circles so, L=√c