the domain of this quadratic relation in my math book is D= {X E R| 2 <_ x <_ 9} and the range is R = {y E R| 1 <_ y <_ 5} but I don't get what the E R means can someone please tell me.
$\displaystyle D = \{x \in \mathbb{R} : 2 \leq x \leq 9\}$
Translation: The domain consists of all x in the set of real numbers such that x is greater than equal to 2 and less than or equal to 9.
$\displaystyle \in$ means 'belongs to'. $\displaystyle \mathbb{R}$ refers to the set of all real numbers.