Some questions ask you to enter an interval of values. To enter your answer, use interval notation.

Use a square bracket if the point is included, parentheses when the point is excluded.

Use U to union two or more intervals.

Use oo (two lowercase o's) for $\displaystyle \infty$, and DNE if the set is empty.

For those not familiar with interval notation, here's some examples of how inequalities can be written in interval notation:

Inequality	Interval Notation
$\displaystyle {4}\le{x}\lt{7}$	[4,7)
$\displaystyle {x}\lt{2}$	(-oo,2)
$\displaystyle {x}\ge{3}$	[3,oo)
all real numbers	(-oo,oo)
$\displaystyle {x}\lt{2}\ \text{or}\ {x}\gt{3}$	(-oo,2)U(3,oo)

Try it out: Write the interval of values shown in the line graph below.



Interval is: