Stage 18 · Circles

18.4.3 How Two Circles Sit Together

18.4 Point, Line, Circle — Who Touches Whom

Point 3 of 4

18.4.3 How Two Circles Sit Together

Core idea

Depending on how near or far they are, two circles can lie outside, touch outside, cross, touch inside, or nest within — all decided by comparing the distance between centers against the sum and difference of the two radii.

Module goal. Use one unifying key — comparing a distance against the radius — to judge how a point, a line, and two circles sit relative to one another.
eastmath.com · 18.4 Point, Line, Circle — Who Touches Whom · 18.4.3 How Two Circles Sit Together