Find the equation of circle concentric with the circle x^2 + y^2 + 4x – 2y + 4 = 0 and 3 times its radius 

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‚ÄčWe have:x2+y2+4x-2y-4=0Center of this cirlce=-42,--22=-2,1As required cirlce is concentric with above cirlce hence centre of required circlewill also be -2,1Let equation of required cirlce be:x-h2+y-k2=r2, where h,k is centre and 'r' is radius.x+22+y-12=r2Radius of x2+y2+2gx+2fy+c=0 is g2+f2-cHence radius of given circle x2+y2+4x-2y-4=0 is:R=22+-12--4=4+1+4=3Radius of required cirlce r=3R=3×3=9Hence required equation of circle is:x+22+y-12=92x+22+y-12=81

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