## Quick Reference

A finite or infinite sequence of terms *a*_{1},*a*_{2},*a*_{3},… with a common difference *d*, so that *a*_{2}−*a*_{1}=*d*, *a*_{3}−*a*_{2}=*d*, and so on. The first term is usually denoted by *a*. For example, 2, 5, 8, 11,…is the arithmetic sequence with *a*=2, *d*=3. In such an arithmetic sequence, the *n*-th term *a*_{n} is given by *a*_{n}=*a*+(*n*−1)*d*.

*Subjects:*
Mathematics.