Question

If a =4 and the sum of first five terms is equal to 1/4th of next five terms .Find the 15th term.

Answer 1

ANSWER :

let the A.P. be a,a+d,a+2d.......

We have T

1

+T

2

+T

3

+T

4

+T

5

=

4

1

[T

6

+T

7

+T

8

+T

9

+T

10

]

∵ sum =

2

n

(first term + last term)

Then

2

5

(T

1

+T

5

)=

4

1

×

2

5

(T

6

+T

10

)

⇒

2

5

(a+(a+4d))=

8

5

[(a+5d)(a+9d)]

⇒2a+4d=

4

1

[2a+14d]

⇒4a+8d=a+7d

⇒d=−3a ....(a=2)

⇒d=−3×2=−6 please Mark as brainlest

Answer 2

Answer:

your answer is in the given attachment :)

Explanation :

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