Question

Write the sum using summation notation, assuming the suggested pattern continues.

-9 - 3 + 3 + 9 + ... + 81

Answer 1

tn=a+(n-1)d
tn=81
a=-9
d=9-3=6
find d
then sum
\[=\frac{ n }{ 2 }\left( a+tn \right)\]

Answer 2

Is this an arithmetic sequence or series, or a geometric sequence or series?
What is the common difference?

Answer 3

Isn't it a geometric sequence? And the common difference is 6.

Answer 4

it is an arithmetic sequence and common difference d=6

Answer 5

Oh. So would i set that up with the Sigma sign?

Answer 6

Would it be this?
\[\sum_{n=0}^{15}(-9+6n)\]

Answer 7

@sleepyjess could you help me with this?