Determine the sum of the following geometric series. Round your answers to 4 decimals if necessary.

a) 50 over sigma k=1 8(.5)^k-2

I assume you mean

50
∑ 8(.5k-2)
k=1

In that case S50 = a(1-r)^50/(1-r)

r = .5
a = 8(1/2^-1) = 16

S50 = 16(.5^50)/.5 = 2^4 * 2^-50 * 2^1 = 2^-45 or 1/2^45