Question

How many terms of the series 54, 51, 48,.........must be taken so that their sum is 513?
Explain the double answer.​

Answer 1

Answer:18, 19

Step-by-step explanation:

= 54 d = -3

Sn = 513

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

513 = n/2( 108 + 3-3n)

1026 = 111 n- 3n^2 =

n^2-37n +342 = 0

on solving, we get n= 18, n=19

We are getting here 2 values, both positive so, Both are applicable here.