The purpose of the Answer Editor for mathematical expressions is to process user input in the form of correct mathematical expressions. One important way in which the Answer Editor guides the user in constructing such expressions is by means of the blue boxes. If a blue box remains on the screen, you know that the input typed so far is not valid.

Entering expressions from the keyboard

For expressions that do not require the use of the Answer Editor keypad, the user can place the cursor within a blue box and enter the mathematical expression from the keyboard. For many expressions, however, the Answer Editor keypad must be used. It may be used, as well, for some types of expressions that can also be entered from the regular keyboard (Fig. 4.2).

Using the Answer Editor keypad to structure simple expressions

To form a simple mathematical expression, the user places the cursor in an empty blue box and clicks on the appropriate button from the Answer Editor keypad. The initial blue box disappears and new blue boxes may appear (depending on the button), accompanied by all of the necessary signs. The user can now fill in the new boxes.

Entering complex expressions

Sometimes it is necessary to enter more complex mathematical expressions. What has been written about entering mathematical expressions into a single blue box holds equally true for entering expressions into any of the blue boxes produced by clicking a button of the Answer Editor keypad. One can place the cursor in one of these boxes and enter an expression from the keyboard, or, by clicking on a button of the Answer Editor keypad, replace it with the structure of a new mathematical expression. Expressions of any degree of complexity can be created in this way. NOTE. The Answer Editor does not supply parentheses. The user must know when these are necessary. In particular, when there is an expression consisting of more than one symbol that must be raised to a power, one may need to enclose it in parentheses, just as in writing; otherwise, only the final symbol (just before the exponent) will be raised to the specified power.

Alternate ways of entering expressions

The buttons of the Answer Editor keypad can be used in other ways as well. In particular, one can select some portion of the input in the entry field which constitutes a complete mathematical expression, and then click on a keypad button. This will create a new mathematical expression within which the expression selected is one component. The same basic rule applies: the minimum unit of manipulation is a complete mathematical expression.

Other mathematical signs

The following mathematical signs can be entered only from the keyboard:

• the plus sign (+);
• the minus sign (-), both for connecting the two parts of a subtraction expression and for designating a negative number;
• the period (.) used in decimals;
• the comma (,) used to punctuate numbers of more than three places.

Please note as well the following special cases:

The asterisk for multiplication

The "x" character on the keyboard cannot be used to enter a multiplication sign. Only the asterisk (*) serves this purpose. (The multiplication sign on the Answer Editor keypad, however, is the traditional x-shaped symbol.)

Mixed numbers

Although fractions can be entered from the keyboard using the front slash character (/), mixed numbers cannot be entered this way. More precisely, the Answer Editor does not automatically regard a whole number followed by a fraction as a mixed number. The mixed number button on the Answer Editor keypad must be used to enter mixed numbers.