The major product formed by the reaction of benzylamine with nitrous acid is

If $f: Z \rightarrow N$ is defined by

$$ f(n)=\left\{\begin{array}{cll} 2 n, & \text { if } & n>0 \\ 1, & \text { if } & n=0, \text { then } f \text { is } \\ -2 n-1, & \text { if } & n<0 \end{array}\right. $$

Domain of $\cos ^{-1}\left[\log _5\left(x^2+7 x+15\right)\right]$ is

Let $f(n)=A(-2)^n+B(-3)^n \forall A, B \in \mathbf{R}$ and $n \in \mathbf{N}-\{1,2\}$. If $f(n)+a f(n-1)+b f(n-2)=0$, then $(a+b)(b-a)=$