Question

find the nth term of an a.p whose sum of the first n terms is 3n

Answer 1

Plz tell your class mate...

Answer 2

Answer:

Step-by-step explanation:

An = 3n+1

put n= 1

A1 = 3 (1)+ 1

= 3+ 1

= 4

===> first term of a.p is 4

put A= 2

A2 = 3(2) + 1

= 6+1

= 7

===> second term of a.p is 7

Common Difference (d ) = A2 - A1

= 7 - 4

= 3

NOW,

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

= n/ 2 [ 2(4) + (n-1) (3) ]

= n /2 [ 8 + 3n - 3 ]

= n / 2 [ 5 + 3n ]

= 5n + 3n^2/2

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Thanks..

hope it will help u .