A set of m linear equations in n unknowns x1, x2,…, xn that has the form
where b1, b2,…, bm are not all zero. (Compare with homogeneous set of linear equations.) In matrix notation, this set of equations may be written as Ax = b, where A is the m × n matrix [aij], and b ≠ 0 and x are column vectors:
Such a set of equations may be inconsistent, have a unique solution, or have infinitely many solutions (see simultaneous linear equations). If m = n, A is square and the set of equations has a unique solution, namely x = A−1b, if and only if A is invertible.