Identify the common external tangent.

line r
line s
segment ab

Line S.
A common internal tangent means that the lines joining the centre touches the tangent. As shown in the diagram, AB, two radii joined together touch the tangent. Hence, it is deemed as a common internal tangent.

However, line S is a common tangent, but lies outside of the centre of the circles, meaning that it is a common external tangent.

Th is not an attachment

Ap human geography and geometry