If the determinant of the system of linear equations having n unknowns and n equations is not equal to zero, then the system of equations has one and only one solution.
If the determinant of the system of linear equations having n unknowns and n equations is not equal to zero, then the system of equations has one and only one solution.
含几个未知量几个方程的线性方程组的行列式，如不为零，则方程组存在一解且仅有一解。