A common way to show multiplication between two variables on a piece of paper is to place them next to each other. For example, expressions like ax or a(x + y) are easily understood to mean “a times x” and “a times the quantity x plus y,” respectively. This cannot be done with Mathcad variables for the simple reason that when you type ax, Mathcad has no way of knowing whether you mean “a times x” or “the variable named ax.” Similarly, when you type a (x+y), Mathcad cannot tell if you mean “a times the quantity x plus y” or whether you mean “the function a applied to the argument

x+y.” In the special case when you type a numerical constant followed immediately by a variable name, such as 4x, Mathcad interprets the expression to mean the constant multiplied by the variable: 4 . x . Mathcad displays a space between the constant and

the variable to indicate that the multiplication is implied. You can produce math notation in this way that closely approximates the notation you see in textbooks and reference books. Note that Mathcad reserves certain letters, such as “i” for the imaginary unit and “0” for octal, as suffixes for numbers, and in these cases will not attempt to multiply the number by a variable name but rather will treat the expression as a single number with a suffix. TO avoid ambiguity, we recommend that you press * explicitly to indicate multiplication, as shown in the following example:

• Type a followed by *. Mathcad inserts a small dot after the “a” to indicate multiplication.

• In the placeholder, type the second factor, x.

**An annotated example**

When it comes to editing equations, knowing how to use the editing lines assumes an importance similar to knowing where to put the flashing vertical bar you see in most word processors. A word processor can get away with a vertical bar because text is inherently one-dimensional, like a line. New letters go either to the left or to the right of old ones. Equations, on the other hand, are really two-dimensional. Their structure is more like a trees with branches than like a line of text. As a result, Mathcad has to use a two-dimensional version of that same vertical bar. That’s why there are two editing lines: a vertical line and a horizontal line. ‘I Suppose, for example, that you want to type the slightly more complicated expression Watch what happens to the editing lines in the following steps: • Type x- 3 *a 1\ 2. Since the editing lines I contain just the “2,” only the “2” be- Ix – 3 . alii comes the numerator when you press the / . Since we want the whole expression,x – 3 . a2 , to be the numerator, we must make the editing lines hold that entire

expression.

• To do so, press the [Space). Each time you press the [Space], the editing lines x – .3, . a2hold more of the expression. You’ll need to press [Space] three times to enclose the entire expression

• Now press / to create a division bar.Note that the numerator is whatever was closed between the editing lines whenyou pressed /.

• Now type -4+ and click on the button labeled “J “on the arithmetic palette.Then type v+ 1 under the radical to complete the denominator.

• To add something outside the radicalsign, press [Space] twice make the editinglines hold the radical. For example,to add the number 1t to the denominator,press [Space] twice.

• Press +. Since the editing lines wereholding the entire radical, it is the entireradical that becomes the first operandwhen you press +.

• Click on the button labeled “rt” on thearithmetic palette. This is one of Mathcad’sbuilt-in variables