0674132人目の素数さん垢版 | 大砲2018/07/25(水) 01:35:01.94ID:9UVBQKrl >>673 訂正スマソ (4mπ/N) → (2(2m-1)π/N) 或いは (弦の長さ) < (2m-1) (幅) = R {1-cos((2m-1)π/N)} < R (1/2) {(2m-1)π/N}^2 (**) = 1/{4sin(π/N)} {(2m-1)π/N}^2 〜 (1/4)(2m-1)^2 (π/N) → 0 (N→∞) **) 1 - (1/2)xx < cos(x) ≦ 1