Question

The expression a1(1−rn)1−r represents the sum of the first n terms of a geometric sequence. The first term is a1, and the the common ratio between terms is r.

What expression represents the sum of the 8th term to the 10th term of the geometric sequence -3,12,-48,...?



Enter a sum or difference that uses the given formula, like 2(1−33)1−3+2(1−35)1−3.