Use the formula for the sum of the first n terms of a geometric sequence to solve. Find the sum of the first 8 terms of the geometric sequence: -8, -16, -32, -64, -128, . . . .
A. -2003
B. -2040
C. -2060
D. -2038

Question

Use the formula for the sum of the first n terms of a geometric sequence to solve. Find the sum of the first 8 terms of the geometric sequence: -8, -16, -32, -64, -128, . . . .
A. -2003 
B. -2040 
C. -2060 
D. -2038

mendicant_bias · Answer

Alright, so all the terms in your sequence have the same sign; you know that they don't alternate. So there's nothing like $$(-1)^n$$involved. You can also see that the terms are doubling with every increase of n, for instance,$$a_{1}=-8,$$$$a_{2}=(2)(-8)=-16,$$$$a_{3}=(2)(-16)=-32,$$$$. \ .\ .\ $$

mendicant_bias · Answer

First, a_n should be found based on the information you can figure out from these terms. Can you find a general formula for a_n?$$a_n=\ ?$$

mendicant_bias · Answer

Since each term increases by two, is there anything you can do with putting two to some power, to get your general formula for a?

midhun.madhu1987 · Answer

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Plug in the values  and find the sum