The terms defined here will be new to at least some readers of Engineers Solve Problems.
Definitions of words in this list often make use of other Glossary terms. Cross-references to defined terms will be indicated by boldface print.
Constant.
A measured quantity that does not change, or that stays the same under particular conditions. A constant is often entered in equations as a letter symbol for convenience.
The acceleration of gravity near the earth's surface is a constant; it is always equal to 32.2 feet per second. Another very familiar constant is the number p (pi), which is the ratio between the circumference and the diameter of a circle.
Cross multiplication.
A method of simplifying an equation in order to solve it for a particular variable or unknown, or in order to show it in a form having fewer fraction. If you multiply (or divide) both sides of an equation by the same amount, the result will still be a correct equation -- that is, the two sides will still be equal. Suppose you know the formula
x/y = w/z
and you also know values for w, y, and z. If you multiply both sides by y, you will have
x = y ? w/z
You can then find x by substituting the three known values. You can also express the original equation without fractions, by multiplying both sides by y and then by z:
x/y = w/z
x = y ? w/z
xz = wy
In each of these examples, cross multiplication was used to change the appearance of the equation.
Equation.
A statement written in numbers and symbols and having two sides connected by an equal sign. The equal sign tells you that the amount represented by all the numbers and symbols on the left is the same as the amount represented by those on the right. For example,
y = 2x + 3
is an equation that tells you how to find the value of y whenever you know the value of x.
Exponent.
A small number placed to the right of and slightly above a number or a letter symbol to show how many times the quantity should be multiplied by itself. Compare square.
Factor.
A single quantity among a group of quantities which when multiplied together will form a given product. The number 6 has the factors 2 and 3. In the expression
2x + 2y
the two terms 2x and 2y each have the factor 2. They are thus said to have a common factor of 2.
Factoring.
Separating a product into the different factors that make it up. This procedure is very useful in solving equations for unknowns. You can factor the expression 2x + 2y to get 2(x + y).
Ratio.
A comparison of two numbers, expressed as the quotient you get by dividing the first by the second. Ratios work the same way as fractions. The ratio of 8 to 2 (also written 8:2) is the same as the ratio of 4 to 1, or simply 4.
Square.
The product you get when you multiply any quantity by itself. Squares are indicated by the exponent 2. For example,
42 = 4 x 4 = 16
and V2, where V = 60 meters per second (m/s), is
V x V = (60m/s)2 = 3600 m2/s2
We read 22 as "two squared" and V2 as "V squared."
Square Root.
A number which when squared will give the desired number. Square roots are shown by a "radical" sign-. The square root of 16, is 4 and appears as follows:
The square root of any number x2 is x. The square root of 2 is not a whole number but is approximately 1.414.
Actually, each of these has both a positive and a negative square root, as you will learn later. Thus the square root of any x2 is +x, and so the square root of 16 is +4.
Subscript.
A small letter or number written or printed to the right of an slightly below a letter symbol. Subscripts may be used, for instance, to identify different variables that are similar enough to each other to have the same main letter symbol.
Unknown.
A variable quantity whose actual value isn't known. An unknown, like a variable, is symbolized in mathematics by a letter.
Variable.
A measurable quantity (such as distance, speed, weight, or temperature) that does not have to have a single, fixed value. For instance, length is a variable because two objects, when measured, may be found to be different in length. A variable is symbolized in mathematics by a letter. Diameter, for example, can be represented by "d." Two very similar variables can be distinguished by subscripts; for example:
d1 = diameter of circle 1 d2 = diameter of circle 2 | 
