Step-by-step explanation:
Geometric Sequence formula for general term:
an = a1(r^n-1)
a1 = 4 × (-5)^1-1
a1 = 4
r = -5
Summation formula for geometric sequence :
Sn = a1 ( 1 - r^n / 1 - r )
...take n from the top of the summation.
= 4 ( 1 -(-5)^6 / 1 -(-5)
= -10416.
