## Elementary Linear Algebra 7th Edition

Since one can see easily that $$\left|\begin{array}{rrr} 0.8& 0.2&- 0.6& 0.1\\ - 1.2& 0.6& 0.6&0\\ 0.7&- 0.3& 0.1&0 \\ 0.2&- 0.3& 0.6&0 \end{array}\right|=0.015,$$ then the matrix $$\left[\begin{array}{rrr} 0.8& 0.2&- 0.6& 0.1\\ - 1.2& 0.6& 0.6&0\\ 0.7&- 0.3& 0.1&0 \\ 0.2&- 0.3& 0.6&0\end{array}\right]$$ is nonsingular.