Use interval notation to indicate all real numbers between and including - 3 and 5

Notations are arbitrary, and you might find different textbooks using different notations.

However, the most common alternatives are:

Using square brackets for included values, and round brackets for excluded values. In this case, your interval is [-3, 5] Using round brackets alone, open towards the number if its included. In this case, your interval is (-3, 5)

For example, if - 3 wasn't included, the two notations would have been (-3, 5] and) - 3, 5)