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Dots in rectangle = n (n1) But remember we doubled the number of dots, so Dots in triangle = n (n1)/2 We can use xn to mean "dots in triangle n", so we get the rule Rule xn = n (n1)/2 Example the 5th Triangular Number is x 5 = 5 (51)/2 = 15 Example the 60th is x 60 = 60 (601)/2 = 10Const proc main is func local var integer num is 0;Problem 42 The nth term of the sequence of triangle numbers is given by, tn = ½ n ( n 1); お母さんが教える子供の算数 お母さんを算数のプロにする計算 文章問題 徹底解説 新版の通販 浜野 克彦 紙の本 Honto本の通販ストア トライアングルナンバーズ 無料