[Math] Algebra 1 – Set builder Notation Domain and Range

algebra-precalculus

I have a quarter 1 test tomorrow and I have looked on many websites containing set builder notation to find domain and range but I still don't understand. Is there anyway to remember it or even how to do it??

Best Answer

If you're given a graph the range is all of the $y$ values and the domain is all of the $x$ values where the graph exists.

For example, consider this graph

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What are the $x$ values at which the function is defined? Well we can see it starts at $-3$ on the left and keeps going until $4$. Notice, that even though this is a piecewise function, every single $x$ between $-3$ and $4$ corresponds to a point on the graph. Then we just need to take into a account whether the endpoints are included or not. In this case $-3$ is but $4$ is not. So the domain, in set builder notation, is $\{x\mid -3\le x\lt 4\}$.

As for the range, we look at the $y$ values. The lowest $y$ value at which the function is defined is $-3$. Then continuing up we see a break from $0$ to $1$. There is no point on the graph that corresponds to $y$ values between those two numbers. But then it continues at $1$ and goes up to $2$. In this case $-3$, $0$, and $1$ are definitely included. It might be slightly harder to tell that $2$is included, but it is. So the range is $\{y \mid -3\le y\le 0 \text{ or } 1\le y \le 2\}$.

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