Question

What is the closed linear form for this sequence given a1 = -15 and an + 1 = an - 8?
A) an = 7 - 8n
B) an = -7 + 8n
C) an = -7 - 8n
D) an = -15 - 8n
my best answer is C

Answer 1

check your first post.

Answer 2

I will interpret that as:
a(1) = -15
a(n+1) = a(n) - 8

so each successive term decreases by 8
y = -8x + b
when x=1, y=-15
-15 = -8+b
b = -7
y = -8x - 7
or
in your variables
a(n) = -8n - 7

"your best answer" was C, correct
There is no "best answer", the others are wrong.

Answer 3

a(n+1) = a(n) - 8
a = -15
arithmetic sequence
see
http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
a = -15
a(n) = -15 -8(n-1)= -15+8 -8n
= -7 -8n
I agree C