VTMO 2026 - Grade 9 - Semifinal - SET 08 - Self-study Question 25

A sequence of circles $(O_1;r_1),(O_2;r_2),(O_3;r_3),\ldots$ is tangent to both sides of angle xOy and adjacent circles, ordered away from O as shown. Given r1=1, r2=2, find r4.