Question

Find the sum of first 8 multiplies of 3

Answer 1

Here first term, a = 3
Common difference, d = 3
Number of terms, n = 8

Sn = n/2(2a + (n-1)d
= 8/2(2x3 + (8-1)3)
= 4(6 + 21)
= 4×27
= 108

Answer 2

the multiples of 3 are
3,6,9,12,15..........
so,this is an ap (sum of 8 multiples)
a=3,d=6-3=3,n=8
S8=n/2[2a+(n-1)d]
S8=8/2[2×3+(8-1)×3]
= 4[6+7×3]
=4[6+21]
=4×27
S8=108