For the following matrix $$\left[ {\matrix{ 1 & { - 1} \cr 2 & 3 \cr } } \right]$$ the number of positive characteristic roots is

Given matrix $$L = \left[ {\matrix{ 2 & 1 \cr 3 & 2 \cr 4 & 5 \cr } } \right]\,\,$$ and $$M = \left[ {\matrix{ 3 & 2 \cr 0 & 1 \cr } } \right]$$
then $$L \times M$$ is

Solve for $$y$$ if $${{{d^2}y} \over {d{t^2}}} + 2{{dy} \over {dt}} + y = 0$$ with $$y(0)=1$$ and $${y^1}\left( 0 \right) = - 2$$

If for a matrix, rank equals both the number of rows and number of columns, then the matrix is called