Plot a single point on number line in interval notation

Question

For example, I want to plot the solution set $\{3\}\cup (2, \infty$). How do I represent 3 as a single point?

Do you want ${3}$ denoted as interval? Then ${3}=[3,3]$. – drhab Sep 05 '15 at 16:57 — drhab, Sep 05 '15 at 16:57

score 7 · Accepted Answer · answered Sep 05 '15 at 16:58

7

The correct notation for a set with only the point $3$ in it is $\{3\}$. If you really want to use interval notation, you could also denote this as $[3,3]$.

Notice that your solution set is just $(2, \infty)$ though, since $3$ is already in the set $(2, \infty)$.

answered Sep 05 '15 at 16:58

Alex G.

8,848

What I meant was how I can plot an individual point on the number line. Sorry if it wasn't clear. – questioner and answerer Sep 05 '15 at 17:38
3

Usually you just draw a dot (i.e. a point) at the point 3 on your number line. – Alex G. Sep 05 '15 at 17:46

score 1 · Answer 2 · answered Sep 05 '15 at 17:51

If you needed to represent $\{2\}\cup(4,\infty)$, then you could use a filled-in dot for individual points, so you might draw something like the following:

As Alex G. mentioned, since $3$ is in $(2,\infty)$, $\{3\}\cup(2,\infty)=(2,\infty)$ so you wouldn't have to do this for the case you mentioned in your original question.

Plot a single point on number line in interval notation

2 Answers2