a circle passes through the point (a,b) and cuts the circle x2+y2=4 orthogonally, then the locus of its centre is?

let the equation of the circle which passes through the point (a, b) is given by:
x2+y2+2gx+2fy+c=0 .....(1)a2+b2+2ga+2fb+c=0......(2)now circle (1) cuts the circle x2+y2=4 orthogonallytherefore2g*0+2f*0=c-4c=4 .....(3)substitute c=4 in eq(2):a2+b2+2g.a+2f.b+4=0now let the centre of the circle by (h,k)therefore h=-g and k=-fthus 

a2+b2-2ha-2kb+4=0 replace h by x and k by y, thus the locus of the centre is:a2+b2-2xa-2yb+4=02(ax+by)-(a2+b2+4)=0
hope this helps you

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