Two circles of radii 20 cm and 5 cm, respectively, touch each other externally at the point P, AB is the direct common tangent of those two circles of centres R and S, respectively. The length of AB is equal to:

15 cm 5 cm 10 cm 20 cm

20 cm

If, r1 = Radius of 1st circle r2 = Radius of 2nd circle Then the direct common tangent = 2 \(\sqrt {r1r2}\)    = 2 \(\sqrt {20 × 5}\)  = 20 cm