Question

1.) write the sum using summation notation assuming the suggested pattern continues 4 - 12 +36 -108 +...

Answer 1

@welshfella @amoodarya

Answer 2

@Michele_Laino @iambatman @ganeshie8

Answer 3

@Astrophysics

Answer 4

Hint:
it is a geometric sequence, whose constant is:
q=-108/36 = 36/(-12) = (-12/4= -3

Answer 5

and first term is a1=4

Answer 6

4(-3)^n or 4(-3)^(n-1)

Answer 7

the n-th term is therefore:
\[\Large {a_n} = {a_1}{q^{n - 1}} = 4 \times {\left( { - 3} \right)^{n - 1}}\]

Answer 8

since we start to count, from n=1

Answer 9

thanks @Michele_Laino

Answer 10

:)