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.

Question 860618: 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.
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!

 

Hi,



6(2a + 11d) = 288

7(2a + 6d = 196 

    2a + 11d = 48

    2a + 6d = 28

           5d = 20

            d = 4  and a = 2 



 = 800

      



 

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