Question

Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .

Answer 1

define a rule of expression that defines the sequence

Answer 2

once you know how to determine {a_n} then summing is simple enough

Answer 3

\[S _{n}=\frac{ n }{ 2 } [2a + (n-1)d]\]

Answer 4

for an arithmetic sequence:\[\sum_{n=a}^b(a_1+d(n-1))=\frac{b(a_1+a_b)}{2}\]

Answer 5

my choice of letters wasnt good lol

Answer 6

n=is the number of terms
a=1st term
d=common difference
Sn=Sum of the n terms

Answer 7

\[\sum_{n=p}^q(a_p+d(n-1))=\frac{q(a_p+a_q)}{2}\]
might be better

Answer 8

ugh ... the range is not q, but q-p ... oh well