If $\begin{vmatrix} ^9C_4 & ^9C_5 & ^{10}C_r \\ ^{10}C_6 & ^{10}C_7 & ^{11}C_{r+2} \\ ^{11}C_8 & ^{11}C_9 & ^{12}C_{r+4} \end{vmatrix} = 0$,then $r$ is equal to:

If ${I_1} = \int\limits_1^{\sin \theta } {\frac{x}{{1 + x^2}}} \,dx$ and ${I_2} = \int\limits_1^{\csc \theta } {\frac{{dx}}{{x\left( {{x^2} + 1} \right)}}}$; then the value of $\left| {\begin{array}{*{20}{c}} {{I_1}}&{I_1^2}&{{I_2}} \\ {{e^{{I_1} + {I_2}}}}&{I_2^2}&{ - 1} \\ 1&{I_1^2 + I_2^2}&{ - 1} \end{array}} \right|$ is

If $A$ is a square matrix of order $3$,then which of the following statements is true? (where $I$ is the identity matrix)

The value of $\left|\begin{array}{lll}1990 & 1991 & 1992 \\ 1991 & 1992 & 1993 \\ 1992 & 1993 & 1994\end{array}\right|$ is

$\left| {\begin{array}{*{20}{c}} 1 & 5 & \pi \\ {{\log }_e}e & 5 & {\sqrt 5 } \\ {{\log }_{10}}10 & 5 & e \end{array}} \right| = $

The determinant of a skew-symmetric matrix of order $3$ is always: