Question

The sum of the first 48 terms of an arithmetic series is 4 times the sum of the first

36 terms of the same series.
Find the sum of the first 30 terms of this series

Answer 1

0 :/

Explanation:

S(48) = (48/2)(2a+47d),

S(36) = (36/2)(2a+35d).

Now S(48) = 4S(36)

24(2a+47d) = 4*18(2a+35d) = 72(2a+35d).

Then 2a+47d = 3(2a+35d) and

6a +105d -2a -47d = 0,

4a +58d = 0,

2a+29d = 0.

Now S(30) = (30/2)(2a+29d) = (15)(2a+29d)=0