Question

PLEASE HELP!!!what is the explicit formula for the sequence7 2 -3 -8 -13

Answer 1

Assuming the index start from $1$, i.e. the first element is $a_1$, the answer is the last one: $a_n = -5n+12$

In fact, the elements of the sequence differ by $5$ units from each other, and are descending, which justify the $-5n$ part.

Nevertheless, the sequence starts from $7$, so when $n=1$ we must have

$-5+k=7 \iff k=12$

hence the formula

$a_n = -5n+12$

Answer 2

It is D.

When you plug in the step number instead of "n" you need to get "a" for your answer.