# Thread: Identify the verbal description on the interval

1. ## Identify the verbal description on the interval

1. (2,4)
2. (-∞, -5)
3. (-9, ∞)

I think I am over-thinking it

1. (2,4)
2. (-∞, -5)
3. (-9, ∞)

I think I am over-thinking it
Well it's not clear what you're being asked to find, but if you just need to verbally describe the interval, I'd go with:

1. $\displaystyle x \in (2,4)$ means x is a real number between 2 and 4 exclusive.
2. ...a real number less than -5.
3. ...a real number greater than -9.

3. The question is unclear, I know. Would it be as simple as, for #1, "right 2, up 4"?

4. These are not ordered pairs! Interval notation provide just another way to indicate a range of numbers. Brackets mean "including", and parentheses mean "not including". You can also rewrite intervals as compound inequalities.

Take a look:
$\displaystyle (a, b)$ is $\displaystyle a < x < b$
$\displaystyle [a, b]$ is $\displaystyle a \le x \le b$
$\displaystyle (a, b]$ is $\displaystyle a < x \le b$
$\displaystyle [a, b)$ is $\displaystyle a \le x < b$
$\displaystyle (-\infty, c)$ is $\displaystyle x < c$
$\displaystyle (-\infty, c]$ is $\displaystyle x \le c$
$\displaystyle (c, \infty)$ is $\displaystyle x > c$
$\displaystyle [c, \infty)$ is $\displaystyle x \ge c$

We never use brackets next to infinity or negative infinity.

Now try rewriting your intervals as inequalities.

5. Thats great. Thank you. Also, it says in some other questions like (exactly like the piece of paper):

#4. 9,10)
#5. -2,1
#6. (-∞, -5

Thats great. Thank you. Also, it says in some other questions like (exactly like the piece of paper):

#4. 9,10)
#5. -2,1
#6. (-∞, -5
These are not well-formed intervals.

7. I know. Would it be a typo? Because I am not understanding why the missing brackets in 4 and 6. And 5 isn't even an interval.

I know. Would it be a typo? Because I am not understanding why the missing brackets in 4 and 6. And 5 isn't even an interval.
Without being able to see your piece of paper, I would say either a typo or a bad photocopy/print-out.

9. I don't have a scanner but I send you to the link of the piece of paper. Its a PDF file. I am 100% it is not a bad photocopy/print-out.

Here is the link. Page 3.

http://susd.desertmountain.schoolfus...682007b4f66e36

I don't have a scanner but I send you to the link of the piece of paper. Its a PDF file. I am 100% it is not a bad photocopy/print-out.

Here is the link. Page 3.

http://susd.desertmountain.schoolfus...682007b4f66e36
Nothing against your teachers, but I think they should have done a better job of proofreading. My guess is that it's supposed to be

[9,10)
[-2,1]
(-∞, -5]

and the [ ] weren't displayed properly, for whatever reason.

11. Alright, thanks. Have a great day.