## Having problems with Df={x|-4<x<} = (4,-4]

Complex numbers, rational functions, logarithms, sequences and series, matrix operations, etc.
chrisdacarnut
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### Having problems with Df={x|-4<x<} = (4,-4]

Df={x|-4<x<} = (4,-4]

I don't understand.

stapel_eliz
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How does your book define "Df"?

The rest just looks like a typoed equivalence, showing the set-builder notation for an interval (assuming the second "less than" is supposed to be a "less than or equal to" sign) and the same interval in interval notation.

jaybird0827
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### Re: Having problems with this.

chrisdacarnut wrote:Df={x|-4<x<} = (4,-4]

I don't understand.

The domain of function $f$ equals the set of all $x$ such that $-4\,\lt\,x\,\lt\,a\,number\,is\,missing$ equals the half-open interval from $4$ to $-4$.

Actually, there are errors. Assuming that the interval part, $(4,-4]$ is correct, the missing number (above) is $4$, and the expression would better look like this:

$\mathbb{D}f\,=\,\{\,x\,|\,-4\,\le\,x\,\lt\,4\}\,=\,[-4,4)$

Comment: $-4$ should be less than or equal to $x$ because the interval is closed at the $-4$ end. Since the same is open at the $+4$ end, that would mean x is less than 4.