Question

What is the explicit formula for this arithmetic sequence? -10,-17, -24, -31, ...

Answer 1

Answer:

D

Step-by-step explanation:

The starting term is a1.

That's the very first term.

a1 = - 10

The second term = -17 which means that you added - 7 to - 10.

So d must be - 7

The formula must be

an = a1 + (n - 1)*d

an = -10 + (n - 1)(-7)

You might wonder why it is n - 1. The reason is because the first term is already added on the right side. The -1 means that we have already included the first term.

We should try the formula out to see what it does. Let's find a4

a4 = -10 + (4 -1)*-7

a4 = -10 + 3(-7)

a4 = -10 - 21

a4 = - 31 which is what the question suggests.