Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

when we say that a solution is true for $-\infty < x < +\infty$ does that mean that it is true for all real numbers or any number between negative infinity and positive infinity, which is quite vague.

share|cite|improve this question
That's the same thing. The set of real numbers is the whole interval $(-\infty,+\infty)$. – 1015 May 10 '13 at 0:05
@julien I think that his/her second interpretation is intended to say "a particular $x$ value in range $(-\infty, +\infty)$". At least, that's how I read it... :) – apnorton May 10 '13 at 0:09
@anorton might very well be right. – 1015 May 10 '13 at 0:11
up vote 2 down vote accepted

When we say solutions exist for $-\infty \lt x \lt +\infty$, we are saying the solution is valid for all $x$ in that range. So, your first statement is the correct interpretation.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.