Hello! Is to prove that the coefficient determinant is non-zero. Multiply the second column by -a and add it to 1 column, the third column by -b and add it to 1 column, and the fourth column by -c and add it to 1 column, and it becomes an upper triangular determinant with the value of -(A 2+B 2+C 2) ≠ 0. The economic mathematics team will help you solve the problem, please adopt it in time. thank you