What is the first term in a geometric sequence if the common ratio is −2 and the sum of the first five terms is 77? Hint: cap s sub n equals start fraction a sub one left parenthesis one minus r to the power of n end power right parenthesis over one minus r end fraction comma r ≠ 1, where a1 is the first term and r is the common ratio. (1 point) a sub one equals start fraction one over seven end fraction a1 = −7 a1 = 3 a1 = 7