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# Chapter 21. Ten Formulas You'll Use Most Often

In This Chapter

• Identifying popular math formulas

• Using common conversion factors

You can find thousands of math formulas. Higher mathematics has many branches, including the study of numbers, sets, probability, and statistics, and they all have formulas. The good news is that technical math uses far fewer formulas, and only a few of those come up all the time. This chapter lists the ten formulas you probably use most frequently and shows you some shortcuts. As a bonus, you often can use one formula two or three ways.

# Area of a Square, Rectangle, or Triangle

In some trades, you find areas all the time, so at some point, you invariably need to calculate the area of a rectangle, square, or triangle (such as to pave a parking lot or landscape a yard). The most common unit of square measure is the square foot. (Chapter 15 gives you more information on areas.)

• Area of a rectangle/square: To calculate the area of a rectangle or a square, the formula is A = L × W, where L is the length and W is the width.

A handy shortcut: When you know two of the terms, you can use this formula to find the third term. If you know the area and the length, you can calculate the width. If you know the area and the width, you can calculate the length.

• Area of a triangle. To calculate the area of a triangle, the formula is where b is the base and h is the height.

As a shortcut, ...

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