What is the formula for the following arithmetic sequence?

-9, -2, 5, 12, ...

an = 9 + (-7)( n - 1)
an = -9 + 7( n - 1)
an = 7 + (-9)( n - 1)
an = -9 + (-7)( n - 1)

an = -9 + 7( n - 1)

Step-by-step explanation:

an = first term + difference (n-1)

First term = 9

Difference = -2 - -9 = -2 + 9 = 7

an = -9 + 7( n - 1)

You can check this by substituting the values in.

a1 = -9 + 7(0) = -9

a2 = -9 + 7(2) = -9 + 7 = -2

a3 = -9 + 7(3) = -9 + 14 = 5