Question

How many terms of the arithmetic progression 2,5,8..Must be taken to get a sum of 392?​

Answer 1

Number of term = 48

Explanation:

GIven:

Arithmetic progression

2,5,8..

Total sum of Arithmetic progression is 392

Find:

Number of term

Computation:

First term a = 2

Difference d = 5 - 2 = 3

Sn = [n/2][2a + (n-1)d]

392 = [n/2][2(2) + (n-1)3]

392 = [n/2][4 + 3n - 3]

784 = [n][1 + 3n]

784 = n + 3n²

3n² + n - 784

n = 48 , n = -49

Number of term = 48