Question

What is the explicit formula for this sequence?

Answer 1

Answer:

$a_n=-7+4(n-1)$

or

$a_n=-7+(n-1)(4)$

Step-by-step explanation:

-7,-3,1,5,... is a arithmetic sequence.

Arithmetic sequences have a common difference. That is, it is going up by 4 each time.

When you see arithmetic sequence, you should think linear equation.

The point-slope form of a line is $y-y_1=m(x-x_1)$.

m is the common difference, the slope.

Any they are using the point at x=1 in the point slope form.  So they are using (1,-7).

So let's put this into our point-slope form:

$y-(-7)=4(x-1)$

$y+7=4(x-1)$

Subtract 7 on both sides:

$y=-7+4(x-1)$

So your answer is

$a_n=-7+4(n-1)$