Exercise 124 Page 241

It is not arithmetic. Let's check if it is geometric.

There is a common ratio between consecutive terms. Therefore this is a geometric sequence.

Recall that an arithmetic sequence increases by a common difference, decreases by a common difference, or is constant. On the other hand, a geometric sequence increases by a common factor, decreases by a common factor, changes sign for each term, or is constant. Examining the sequence, however, we see that it first decreases from $1$ to $0$ and then it increases from $0$ to $1.$ Also, the next term is not the result of the previous term multiplied by the constant factor. Therefore, it is neither geometric nor arithmetic.

There is a common difference, and therefore this sequence is arithmetic.