The natural numbers are divided into groups as (1), (2, 3, 4), (5, 6, 7, 8, 9), ….. and so on. Then, the sum o

Question

The natural numbers are divided into groups as (1), (2, 3, 4), (5, 6, 7, 8, 9), ….. and so on. Then, the sum of the numbers in the 15th group is equal to

Accepted Answer

6119. The first number in each group: 1, 2, 5, 10, 17..... Their common difference is in Arithmetic Progression. Hence, the general term of the series can be expressed as a quadratic equation. Let the quadratic equation of the general term be a x 2 + b x + c ax^2+bx+c a x 2 + b x + c 1st term = a+b+c=1 2n