If the lines $x + 2ay + a = 0$, $x + 3by + b = 0$  and $x + 4cy + c = 0$ are concurrent, then $a$, $b$ and $c$ are in

The system of equations $\lambda x + y + z = 0,$ $ – x + \lambda y + z = 0,$ $ – x – y + \lambda z = 0$, will have a non zero solution if real values of $\lambda $ are given by

$\left| {\,\begin{array}{*{20}{c}}1&a&b\\{ – a}&1&c\\{ – b}&{ – c}&1\end{array}\,} \right| = $

Let $[.]$ , $ \{.\} $ and $sgn$$(.)$ denotes greatest integer function, fractional part function and signum function respectively, then value of determinant

$\left| {\begin{array}{*{20}{c}}
  {\left[ \pi  \right]}&{amp(1 + i\sqrt 3 )}&1 \\ 
  1&0&2 \\ 
  {\operatorname{sgn} ({{\cot }^{ – 1}}x)}&1&{\{ \pi \} } 
\end{array}} \right|$ is-

Let the system of linear equations  $x+y+k z=2$ ;  $2 x+3 y-z=1$ ; $3 x+4 y+2 z=k$ , have infinitely many solutions. Then the system $( k +1) x +(2 k -1) y =7$ ; $(2 k +1) x +( k +5) y =10 \text { has : }$