SOLUTION: The sum of the first seven terms of an AP is 98 and the sum of the first twelve terms is 288.Find the sum of the first twenty terms.

Algebra ->  Sequences-and-series -> SOLUTION: The sum of the first seven terms of an AP is 98 and the sum of the first twelve terms is 288.Find the sum of the first twenty terms.       Log On

 

Hi,



6(2a + 11d) = 288

7(2a + 6d = 196 

    2a + 11d = 48

    2a + 6d = 28

           5d = 20

            d = 4  and a = 2 



 = 800