3+15+75+.....+46875
a1 = first term = 3
If we multiply the first term by 5, we obtain the second term.
3 x 5 = 15
15x 5 = 75
75x 5= 375
375x5= 1875
1875x5=9375
9375x5= 46875 (7th term) n=7
So,
r= 5
Apply the formula:
an= a1 * r^(n-1)
an= 3 * 5 (n-1)
Sum
Sn = a1 (1 -r^n) / 1- r
S(7) = [3 (1 - 5^7)] / 1-5
S(7) = [3 (1-78,125)] /-4
S(7) = 58,893
