A set of linear equations is represented by the matrix equations $$Ax=b.$$ The necessary condition for the existence of a solution for this system is

If the vector $$\left[ {\matrix{ 1 \cr 2 \cr { - 1} \cr } } \right]$$ is an eigen vector of $$A = \left[ {\matrix{ { - 2} & 2 & { - 3} \cr 2 & 1 & { - 6} \cr { - 1} & { - 2} & 0 \cr } } \right]$$ then one of the eigen value of $$A$$ is

The $$MOSFET$$ switch in its on - state may be considered equivalent to

In a commutation circuit employed to turn off an $$SCR$$, Satisfactory turn-off is obtained when.