Interval notation infinity

In a math class of mine, two people were having an argument and their views were as follows:

I think that the domain for lets say the graph y=x in interval notation is (-♾, ♾).

I think it should be [-♾,♾]

I personally believe it should be shown as (-♾,♾) because interval notation states the two ends like a direction, especially when you include ♾. Since a direction is not a specific point, you would use (), not []. This is just my reasoning, and I would like to hear more opinions on the matter.

Note: with interval notation, you use ) or ( when it ends at point but does not include that point, and you use ] or [ when the point is included.

#Algebra

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Comments

Your reasoning is correct. Infinity is not a number, so we can't really include it in the endpoints of our interval....

Aaghaz Mahajan - 1 year, 8 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$