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bhargavi (67)

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considering     the line  of centres  to be the x- axis,  & the distance  between the  centres  as 2t   c1=(t,0)   c2=(-t,0)
     s1=(x-t)2+y2=r2         s2=(x+t)2+y2=R2
now   s1/r +/- s2/R=0     implies    Rs1+/-rs2=0
Rs1+rs2=0  becomes    x2+y2-2t(R-r/R+r)x+t2-rR=0.......[1]
Rs1-rs2=o   becomes    x2+y2-2t(R+r/R-r)x+t2+rR=0......[2]
from   [1]&[2],   2g1g2+2f1f2=2[-t(R-r)/R+r][-t(R+r)/R-r]=2t2=(t2-Rr)+(t2+Rr)=c1+c2
 2g1g2+2f1f2=c1+c2  implies    the 2 circles  are  orthogonal
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