** C.
Other Keys**

4. Comma, Parentheses, Brackets, Equal

The comma, parentheses, and bracket keys are frequently used in operations on the TI-89. Expressions are evaluated according to the standard hierarchy of operations, so it is necessary to use parentheses to change this order. The comma is used when entering different operations. Brackets, both curly and square, are also used in entering operations. The comma key and parentheses keys are main functions because they are used so often. This makes them easy to access. The curly brackets, which are primarily used in lists, and the brackets, which are primarily used with matrices, are secondary functions and you will have to use the key to access them.

The equal operation is used to test whether two expressions, lists, or matrices are equal. To view this along with other test operations, click here.