Question

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Answer 1

You have the following formula for the sum Sn:

`S_n=(a_1-a_nr)/(1-r)`

a1 = 4

an = 128

r = 2

replace the previous values into the formula for Sn:

`S_n=(4-128\cdot2)/(1-2)=252`

Hence, the asnwer to Sn is 252