Intro to Millwright Practice Exam

What is used to find the missing length of one side of a right angle?

1. Pythagorean theorem

2. 3, 4, 5 rule

3. Law of cosines

4. Square root method

The correct answer is: 3, 4, 5 rule

The 3, 4, 5 rule is a practical method used in construction and carpentry to create right angles by leveraging the properties of a right triangle. In this rule, if one side of a right triangle is 3 units long and another side is 4 units long, the hypotenuse will be 5 units long. This relationship is derived from the Pythagorean theorem, which states that the sum of the squares of the two shorter sides equals the square of the hypotenuse. Using the 3, 4, 5 rule offers an intuitive and easy way to ensure right angles without complex calculations, making it particularly useful on job sites where quick measurements are needed. To apply it, you measure and mark one side 3 units, another side 4 units, and then ensure the diagonal distance between those two marks is exactly 5 units. If not, adjustments can be made until the relationship holds. While the Pythagorean theorem is certainly relevant in this context, the 3, 4, 5 rule simplifies its application into a straightforward method usable in practical scenarios. The other methods listed, such as the law of cosines, involve more complex calculations that are generally not necessary when establishing