finding values for x

[maths12345]

Hi, i have linked a question and its answer below. What does x E R mean (the final answer)?
Could someone please explain how you know the answer is this value?


Thank you for all your help.

 

[Deleted member 4993]

Hi, i have linked a question and its answer below. What does x E R mean (the final answer)?
Could someone please explain how you know the answer is this value? Thank you for all your help.

Short translation is:

For all x in real domain.

Can (1-x)² be negative for any real value of x?

 

[pka]

\(\displaystyle f(x)\) is increasing for \(\displaystyle x\) in the set of real numbers.