Lines: , , . Slopes are decreasing (sorted). Build the lower envelope. Add line 1 (): deque = [L1]. Add line 2 (): check if L1 is still useful.
Intersection at . L2 better for . Deque = [L1, L2]. Add line 3 (): L3 intersects L2 at . L3 intersects L1 at . L2 is dominated: remove it. Final deque = [L1, L3]. Query : L1 gives , L3 gives . Min = 22 from L1. Deque structure gives amortized query.