Question

What is the sum of a sequence that has 9 terms beginning with 4, 12, 36,...?

Answer 1

@phi

Answer 2

@lgbasallote sorry I don't understand this one either.

Answer 3

first find the 9th term

Answer 4

So I'd use an=a1(n-1)d right

Answer 5

an = a1 + (n-1)d

Answer 6

What do I sub for D though?

Answer 7

hmm wait... this is not arithmetic sequence

Answer 8

this is geometric sequence

Answer 9

exactly why i'm lost

Answer 10

unfortunately i dont have the formula for sum of geometric sequence memorized

but to find the 9th term you use the formula
\[a_n = a_1 r^{n-1}\]

Answer 11

What is r?