Write out the first three terms and the last term of the arithmetic sequence.
-$$\sum _ { i = 1 } ^ { 70 } - 2 i$$
A) $- 2 + 4 - 12 + \ldots - 280$
B) $- 1 - 2 - 4 - \ldots - 140$
C) $- 2 - 4 - 8 - \ldots - 280$
D) $- 2 - 4 - 6 - \ldots - 140$

Question

Quizplus · Accepted Answer

The given sequence is an arithmetic sequence where each term is obtained by subtracting 2 times the position of the term. The first term is $-2 \times 1 = -2$, the second term is $-2 \times 2 = -4$, and the third term is $-2 \times 3 = -6$. The last term, when $i = 70$, is $-2 \times 70 = -140$. This matches option D.

Write Out the First Three Terms and the Last Term ∑i=170−2i\sum _ { i = 1 } ^ { 70 } - 2 ii=1∑70​−2i

Write Out the First Three Terms and the Last Term $\sum _ { i = 1 } ^ { 70 } - 2 i$