Question

Find the sum of the infinite geometric series, if it exists.

Answer 1

first, determine the ratio (r) of that series,
r = a2/a1 = -1/4

Answer 2

then use the formula :
S = a/(1 - r)
with a is the first term, r = ratio
S = a/(1 - r)
= 4/(1 - (-1/4))
= 4/(1 + 1/4)
= 4/(5/4)
= 4 * 4/5
= 16/5

Answer 3

Thanks