Question

find the sum of the first 10 terms of the series 2-6+18-54+...

Answer 1

have you studied arithmetic and geometric progressions?

Answer 2

@kat762 if you have, then try and spot what type of series this is: 2, -6, 18, -54, ...

Answer 3

you have an geometric series . The difference is a2 /a1 = -6/2 = -3
sn = a1 (1 - r^n)/(1 - r)
n = 10
a1 = 2 (first term)
r = -3