A tridiagonal matrix is one where the only nonzero elements are the ones on tridiagona In this case, Gauss elimination can be made much more efficient because most elements are already zero and don't need to be modified or added. (b) Consider a linear system Ax - b with 100,000 unknowns and the same number of equations. The coefficient matrix A is tridiagonal, with all elements on the main diagonal equal to 3 and all elements on the diagonals above and below it equal to 1. The vector of constant terms b contains all ones, except that the first and last elements are zero. Give the value of the first unknown, x1