S = пR^2 = п (C/2п)^2 = C^2/4п = 12.56^2/4*3.14=12,56^2/12,56 = 12,56 дм2
S=πr² C=2πr ⇒ r=C:(2π) π * C² π * C² C² 12,56 * 12,56 12,56 * 12,56 S = ---------- = --------------- = ---------- = ------------------- = ---------------------- = 12,56 (дм²) (2π)² 4 * π² 4 * π 4 * 3,14 12,56