The matrix $$\left[ {\matrix{ 1 & { - 4} \cr 1 & { - 5} \cr } } \right]$$ is an inverse of the matrix $$\left[ {\matrix{ 5 & { - 4} \cr 1 & { - 1} \cr } } \right]$$

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

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

The composition of an oxy-acetylene flame for cutting of steel contain more oxygen.