Posted by **Jen** on Tuesday, June 2, 2009 at 11:25pm.

Please solve for the interval notation corresponding to the set notation

{x | x < –7}

- Algebra -
**MathMate**, Tuesday, June 2, 2009 at 11:29pm
See answer to Rachale's question.

http://www.jiskha.com/display.cgi?id=1243987256

- Algebra -
**Jen**, Tuesday, June 2, 2009 at 11:32pm
Thank you, but why is it

(-infinity -7)?

is it translated to

negative infinity - 7?

- Algebra -
**MathMate**, Tuesday, June 2, 2009 at 11:38pm
> [-5,8) is the same as {x|-5=<x<8}

meaning that the square bracket [ includes the lower limit, while the ] includes the upper limit. The limits are separated by a comma.

You are right in actual practice, it is normal to exclude infinity or negative infinity. In my books, -infinity is a short form for negative infinity.

So the correct answer would be:

**(negative infinity, -7)**

- Algebra -
**Jen**, Wednesday, June 3, 2009 at 12:05am
Thank you for the explanation!

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