If  P (1, 1/2) is a centre of similitude for the circles x2+y2+4x+2y−4=0 and x2+y2−4x−2y+4=0, then the length of the common tangent through P to the circles, i

Clearly, P (1, 1 I 2) is the internal centre of similitude. Thus, if PT1 fi and PT2 are the lengths of tangents drawn from P to the given circles, then Length of the common tangent =PT1+PT2=32+12=2