find the sum of the first 9 terms of the geometric series 1

find the sum of the first 9 terms of the geometric series:

1 - 4 + 16 - 64 .......

1 - 4 + 16 - 64 ...

sum of geometric series is given by the formula

Sn = a1 ( 1- r^9 ) / ( 1- r)

r = common ratio which is -4/1 = -4

a1 = first term

n = number of terms

plugging the values in the fromula

Sn = 1 ( 1- (-4)^9) ( 1- (-4)

S9 = 52429

therefore, sum is 52429