Answer:
Explanation:
This is an arithmetic sequence because each term subtracted by the previous term is a constant called the common difference.
an=a+d(n-1) where a is the initial term and d is the common difference
a=-20 and d=-16+20=4 so
an=-20+4(n-1)
an=4n-24
The sum of an arithmetic sequence is the average of the first and last terms times the number of terms
sn=(a1+an)(n/2)
s30=(-20+4(30)-24)(30/2)
s30=1140