When two circles of radii r1 and r2 have their centres at a distance d apart, then length of the common transverse tangent is:
1
\(\sqrt{d^2 - (r_1 - r_2)^2}\)
2
\(\sqrt{d^2 + (r_1 - r_2)^2}\)
3
\(\sqrt{d - (r_1 - r_2)^2}\)
4
\(\sqrt{d^2 - (r_1 + r_2)^2}\)