What is the difference between... these two intervals

Printable View

• Oct 6th 2012, 07:18 PM
Eraser147
What is the difference between... these two intervals
When dealing with inequalities like this Attachment 25088, Attachment 25089 The problem states that I need to write the given set as an interval or a union of two intervals. Are the answers above both correct? Click image to enlarge please.
• Oct 6th 2012, 08:08 PM
Soroban
Re: What is the difference between... these two intervals
Hello, Eraser147!

Quote:

When dealing with inequalities like this: .$\displaystyle |x+4| \:<\:\tfrac{1}{200}$

The problem states that I need to write the given set as an interval or a union of two intervals.

Are both these answers correct?

. . $\displaystyle \left(-\tfrac{801}{200},\,-\tfrac{799}{200}\right)$ . . . . $\displaystyle \left(-\infty,\,-\tfrac{801}{200}\right) \:\cup\:\left(-\tfrac{799}{200},\,\infty\right)$

Obviously, both of them cannot be correct.

Here is helpful rule.

We have an inequality with an absolute value.

If the inequality is "less than", $\displaystyle |x| \:{\color{red}{<}}\: a$
. . then $\displaystyle x$ is between $\displaystyle \text{-}a$ and $\displaystyle +a$.
This is written: .$\displaystyle \text{-}a \,<\,x\,<\,a$

If the inequality is "greater than", $\displaystyle |x|\:{\color{red}{>}}\:a$
. . then $\displaystyle x$ is "outside" of $\displaystyle \text{-}a$ and $\displaystyle +a$.
This is written: .$\displaystyle x\,<\,\text{-}a\;\cup\;x\,>\,a$

• Oct 6th 2012, 08:28 PM
Eraser147
Re: What is the difference between... these two intervals
Very helpful, thank you very much.