Arrange the natural numbers starting from 1 in the following order one 2 3 4 5 6 7 8 9 10 The first number in line n is The last number of N rows is The sum of the numbers in line n is

Arrange the natural numbers starting from 1 in the following order one 2 3 4 5 6 7 8 9 10 The first number in line n is The last number of N rows is The sum of the numbers in line n is

Line n-1 before line n, 1 + 2 + 3 + +(n-1) = (1 + n-1) (n-1) / 2 = n (n-1) / 2 numbers
be
The first number in the nth row = n (n-1) / 2 + 1
The last number in line n = (n + 1) (n + 1-1) / 2 = n (n + 1) / 2
The sum of the numbers in line n
= [N(N-1)/2 + 1 + N(N+1)/2 ] * N / 2
= (N² + 1) * N / 2