Equation of a circle with centre (2, 1) and which cuts off a chord of length 4 on the line 3x+4y−5=0  is

d=perpendicular distance from centre (2,1) = (x1,y1) of the circle to the chord 3x+4y-5=0d=ax1+by1+ca2+b2d=|6+4−5|25=1we have length of the chord is 4=2r2-d22=r2-d24=r2-d2r=d2+4=5∴(x−2)2+(y−1)2=5⇒x2+y2−4x−2y=0