নিচের কোনটি ফাংশন নয়?

If $f\left(x+\dfrac{1}{x}\right)=x^2+\dfrac{1}{x^2}$ then $f(x)=?$

Let $A$ be set of first ten natural numbers and $R$ be a relation on $A$ defined by (x , y) $\in$ $R$ $\Rightarrow$ x + 2y = 10 , then domain of $R$ is

If $  A  $ is a finite set containing n distinct elements, then the number of relations on A is equal to