, , ,

This is an arithmetic sequence since there is a common difference between each term. In this case, adding to the previous term in the sequence gives the next term. In other words, .

Arithmetic Sequence:

This is the formula of an arithmetic sequence.

Substitute in the values of and .

Apply the distributive property.

Multiply by .

Subtract from .

Identify the Sequence 3 , 9 , 15 , 21