Calculus with Applications (10th Edition)

$x\leq3$
[ ] is equivalent to the greater/less than and equal to $\leq$ and $\geq$ signs ( ) is equivalent to the greater/less than $\lt$ and $\gt$ signs Thus from the information given x is less than or equal to 3 $x\leq3$ The other information given by the interval notation is x is greater than negative infinity In this case we don't have to write out $-\infty$$\lt$x because in writing just $x\leq3$ it includes all numbers below or equal to 3