Question

if the sum of n terms of an arithemetic prograssion 2,5,8,.... is equal to the sum of first n terms of another arithemetic prograssion 57,59,61,... then find the value of n?​

Answer 1

Answer:

11

Step-by-step explanation:

The sum of first 2n terms of 2,5,8,... is

=

2

2n

[2(2)+(2n−1)(3)]

=n(6n+1)

The sum of n terms of 57,59,61,... is

=

2

n

[2(57)+(n−1)(2)]

=n(56+n)

Also, n(6n+1)=n(56+n)

⇒6n+1=56+n

⇒5n=55

⇒n=11