If $\left| {\begin{array}{*{20}{c}}
  {^9{C_4}}&{^9{C_5}}&{^{10}{C_r}} \\ 
  {^{10}{C_6}}&{^{10}{C_7}}&{^{11}{C_{r + 2}}} \\ 
  {^{11}{C_8}}&{^{11}{C_9}}&{^{12}{C_{r + 4}}} 
\end{array}} \right| = 0$ then $r$ is equal to 

For the system of linear equations

$2 x-y+3 z=5$

$3 x+2 y-z=7$

$4 x+5 y+\alpha z=\beta$

Which of the following is NOT correct ?

Find area of the triangle with vertices at the point given in each of the following: $(1,0),(6,0),(4,3)$

Number of values of $m$ for which the lines $x + y - 1 = 0$, $(m - 1) x + (m^2 - 7) y - 5 = 0 \,\,\&\,\, (m - 2) x + (2m - 5) y = 0$ are concurrent, are

If $A \ne O$ and $B \ne O$ are $ n × n$ matrix such that $AB = O,$ then

Consider the system of linear equation $x+y+z=$ $4 \mu, x+2 y+2 \lambda z=10 \mu, x+3 y+4 \lambda^2 z=\mu^2+15$, where $\lambda, \mu \in R$. Which one of the following statements is $NOT$ correct?