Use the Formula for the Sum of the First n Terms of an Arithmetic Sequence
-Find the sum of the first 30 terms of the arithmetic sequence: 18, 24, 30, 36, . . .
A)3150
B)3159
C)198
D)3240

Question

Quizplus · Accepted Answer

The correct answer is A.The formula for the sum of the first n terms of an arithmetic sequence is:Sn = n/2 * (a1 + an)where Sn is the sum of the first n terms, a1 is the first term, an is the nth term, and n is the number of terms.In this case, a1 = 18, an = 18 + (30 - 1) * 6 = 18 + 17 * 6 = 126, and n = 30.So, Sn = 30/2 * (18 + 126) = 15 * 144 = 2160.Therefore, the sum of the first 30 terms of the arithmetic sequence is 2160.

Use the Formula for the Sum of the First N