If $$\left[ {\matrix{ {3c + 6} & {a - d} \cr {a + d} & {2 - 3b} \cr } } \right] = \left[ {\matrix{ {12} & 2 \cr { - 8} & { - 4} \cr } } \right]$$ are equal, then value of ab $-$$ cd is

The principal value of $${\tan ^{ - 1}}\left( {\tan {{9\pi } \over 8}} \right)$$ is

For two matrices $$P = \left[ {\matrix{ 3 & 4 \cr { - 1} & 2 \cr 0 & 1 \cr } } \right]$$ and $${Q^T} = \left[ {\matrix{ { - 1} & 2 & 1 \cr 1 & 2 & 3 \cr } } \right]$$ P $$-$$ Q is

The function $$f(x) = 2{x^3} - 15{x^2} + 36x + 6$$ is increasing in the interval