Question

The 14th term of on Ap is twice its 8th term.if it's 6th term is -8, then find the sum of its first 20 terms
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Answer 1

Answer :

14th term, A14 = a + 13d

8th term, A8 = a + 7d

➡️ A14 = 2 A8

=> a + 13d = 2 ( a + 7d)

=> a + 13d = 2a + 14d

=> a = - d

6th term, A6 = a + 5d

-8 = a + 5d

-8 = - d + 5d

4d = - 8

d = - 8/4 = - 2

➡️ d = - 2

=> a = - d = - ( - 2)

➡️ a = 2

S20 = n/2 [ 2a + ( n - 1) d]

S20 = 20/2 [ 2*2 + 19* ( - 2)]

S20 = 10 [ 4 - 38]

S20 = 10 *( - 34 )

S20 = - 340

Answer 2

Hey there Guys !!

Refer to the Attached pic

Hope this is gonna help you ! ☺

@A❤sh_30