Question

120
∑ (3n-6)
n=1
Find the sum.

Answer 1

21300

Explanation:

120∑n=13n−4

Split the summation into smaller summations that fit the summation rules.

120∑n=1 3n−4=3120∑n=1 n+120∑n=1 −4

Evaluate

3120∑n=1 n.

21780

Evaluate

120∑n=1 −4 −480

Add the results of the summations.

21780−480

Subtract 480 from 21780.

21300