If $f(x+y)= f(x) + f(y) -xy-1$ for all x, y and f(1)=1 then the number of solution of $f(n)=n,n\in N$ is

Let $\displaystyle R = \{(x, x + 5) : x \in \{0,1, 2, 3, 4, 5\} \}$

Find dom $\displaystyle (R)$ and range $\displaystyle (R)$. And enter the common element between them.

Let A and B be two sets containing four and two elements respectively. Then the number of subsets of the set $A \times B$, each having at least three elements is............

If $A = \{ 1,2,3,4,5,6 \} , B = \{ 1,2 \} ,$ then $\frac { A } { \left( \frac { A } { B } \right) }$ equal to 

$13$ Planar Surfaces, each of area $1\ m^{2}$ are such that their total area is $7\ m^{2}$. If no three of more of these surfaces have any region in common; Then, the overlap of some Two of These surfaces has an Area.