Question

Find the sum of the first n terms of A.P 1,4,7,10,.......find S15​

Answer 1

Answer:

heya mate there's your answer

Given series of AP is 1,4,7,10..........

let first term of the AP be a1 =1

second term of the AP be a2=4

andcommon difference of the AP be d

d=a2-a1

d=4-1

d=3

so common difference of the AP is d=3

sum of n terms in an AP is,

Sn=n/2[2a1+(n-1)d]

so, S15=15/2[2×1+(15-1)(3)]

=15/2[2+14(3)]

=15/2[2+42]

=15×44/2

=15×22

=330

So S15=330

hope it helps you..........

Thank you!!!

Answer 2

Answer:

a=1 and d=3

S=330

S=(n/2)(2a+(n-1)d)

S=(15/2)2+42

S=15*44/2

S=22*15

S=330

This is your answer