Question

if tn= 2 + 3n, then find the sum of first 7 term of AP

Answer 1

Heya !!!


Tn = 2 + 3N



T1 = 2 + 3 × 1



=> 2 + 3


=> 5




And,



T2 = 2 + 3 × 2


=> 2 + 6


=> 8


T3 = 2 + 3 × 3



=> 2 + 9


=> 11



AP= 5 , 8 , 11 ......


Here,



First term ( A) = 5


Common Difference (D) = 8-5 = 3



Sn = N/2 × [ 2A + ( N-1) × D ]


S7 = 7/2 × [ 2 × 5 + ( 7-1) × 3 ]





=> 7/2 × ( 10 + 18)




=> 7/2 × 28




=> 7 × 14



=> 98




HOPE IT WILL HELP YOU...... :-)