มันทำอันนี้ได้ไหมครับช่วยลองหน่อย Delta*x = 3/n , x_{n} = 3 , C₁ = X₁-1 sum i = 1 to n f(c_{i}) * Delta*x = sum i=1 ^ n f(x i-1 ) Delta x= sum i=1 ^ n (9-x i-1 ^ 2 ) Delta = sum i = 1 to n [9 - ((3(i - 1))/2) ^ 2] * 3/n = sum i = 1 to n (27/n - (27i ^ 2)/(n ^ 3) + (54i)/(n ^ 3) - 27/(n ^ 3)) = 27/n * sum i = 1 to n 1 - 27/(n ^ 3) * sum i = 1 to n i ^ 2 + 54/(n ^ 3) * sum i = 1 to n i - 27/(n ^ 3) * sum i = 1 to n 1 = 27/n * (n) - 27/(n ^ 3) * ((n(n + 1)(2n + 1))/6) + 54/(n ^ 3) * ((n(n + 1))/2) - 27/(n ^ 3) * (n) = 18 + 27/(2n) - 9/(2n ^ 2) R = lim n -> ∞ sum i = 1 to n f(c_{i}) * Delta*x = lim n -> ∞ (18 - 27/(2n) - 9/(2n ^ 2)) =
