Answer:
-1,512,390
Step-by-step explanation:
Given
a1 = 15
Let us generate the first three terms of the sequence
For
Hence the first three terms ae 15, 8, 1...
This sequence forms an arithmetic progression with;
first term a = 15
common difference d = 8 - 15 = - -8 = -7
n is the number of terms = 660 (since we are looking for the sum of the first 660 terms)
Using the formula;
Substitute the given values;
Hence the sum of the first 660 terms of the sequence is -1,512,390