[High School Math] How to find the Domain of something that isn't a fraction.
Finding Domain of Functions: Do you only solve the top expression of a radical function when it has square root in the numerator?
algebra precalculus - How can I get the domain of a fraction under a square root? - Mathematics Stack Exchange
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I know that the general process of finding the Domain of an expression (when it is a fraction) is merely that the denominator can't equal zero, so in the case of something like:
1/x + 3
It just becomes a matter of solving x + 3 = 0.
But what would I do in the case that have I something that isn't a fraction, like this:
x + 2 = 1 + sqrt(2 + x)
or x - sqrt(2 - x)
I'm learning to find the domain of functions. I've noticed, iirc, that the top expression seems to be ignored and only the denominator is solved to find the domain. It's not until there is a square root in the numerator that the top expression is solved for in order to be included in the domain. What is the reasoning for this if that's the case?
I usually start by assuming the domain is all real numbers, then removing the values of $x$ that don't make sense. What remains is the domain. In your case, if $x=0$ then you are dividing by zero. That's bad, so remove $x=0$ from the domain. What else can go wrong? Taking the square root of a negative number will cause problems (unless you're working in the complex numbers). So figure out when is $1 + \frac{1}{x} < 0$. All those values of $x$ are not in the domain.
Hint:
Basically, the conditions are $$x\ne 0\quad\text{and}\quad 1+\frac 1x=\frac{x+1}x\ge 0. $$ Now the sign of the fraction is the sign of the product $x(x+1)$, and you have a theorem about the sign of a quadratic polynomial…