People sometimes describe trigonometry as the science of circles and angles. It's trigonometry that helps you calculate the hypotenuse of a triangle or the diameter of a circle. However, when you use trigonometry in Excel, you probably won't be worrying about shapes; instead, you'll be using some type of formula from a scientific field that requires common trigonometric calculations like the cosine or tangent.
Students of the sciences know that trigonometry turns up anywhere you need to think about space, including geography, astronomy, kinematics, and optics. Less direct applications of trigonometry turn up in just about every other scientific field—from chemistry to social science.
You can use Excel's trigonometric functions quite easily. Just choose the formula you need and the appropriate argument, much as you'd use a pocket calculator. (Knowing when to use these trigonometry functions is another issue, and it may require a refresher course in mathematics.) Table 9-1 lists the functions you can use. Figure 9-11 shows how you can use trigonometry to solve a common high-school math problem: you have the distance to a tree (which you can easily measure), and the angle between your current position and the top of the tree (which you can estimate). The problem is you have no way to judge the height of the tree.
Table 9-1. Trigonometry functions
Calculates the inverse cosine (also known as the arccosine) of a number. ...