Suppose v1, ..., vn are vectors. We define a linear combination of v1, ..., vn to be a sum a1v1+...+anvn where a1, ..., an are scalars. In this context, we refer to a1, ..., an as the coefficients in this linear combination. In particular, a1 is the coefficient of v1 in the linear combination, a2 is the coefficient of v2, and so on.