Question

if the first term of the AP is 4and the sum of the first five terms is equal to one-fourth of the sum of the next five terms then find the fifteenth term​

Answer 1

Step-by-step explanation:

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

Answer 2

Answer:

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