446. Two circles are given. We want to draw a common tangent - a line that touches both circles. How many such lines exist? (The answer depends on the ratio of the radii of the circles and the distance between their centers.)
$\triangleright$ Let the radii of the circles be $r$ and $R$ (assuming $rR+r$ there are four tangents - two external and two internal. $\triangleleft$

A common tangent to two circles can be external (both circles lie on the same side of the tangent) or internal (the circles lie on opposite sides).

