Math, asked by vyeshwanth56, 8 months ago

the sum of 5th and9th term is 40 and sum of 8th and 14th term is 64. find S 20

Answers

Answered by tejaspaunikar2716
1

Answer: 240

we know that Snth=N/2[2A+(N-1)D]

Step-by-step explanation:

Let a be the first term and d be the common difference of the AP.

Then, A/Q

(a + 4d) + ( a + 8d) = 40

a + 6d = 20 ......(i)

and, (14/2)(2a + 13d) = 64

2a + 13d = 64/7 ........(ii)

By solving equation (i) and (ii) , we get

a = 236/7

and d = -16/7

Therefore, Sum of first 20 terms are

(20/2)(2*(236/6) + 19(-16/7))

=240

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