What is a law or rule expressed as an equation?

• A. Expression
• B. Theorem
• C. Formula
• D. Principle

Answer: (C)

A formula is specifically defined as a mathematical relationship or rule expressed in symbols. It usually represents a general principle that can be applied to solve problems or calculate specific values by substituting known quantities into the equation. For instance, in the realm of pipefitting, formulas can be used to calculate the pressure drop in a piping system or the flow rate of fluids.

An expression, while also a mathematical term, does not convey a complete relationship since it may not include an equal sign or indicate a rule that can be directly applied for calculations. A theorem is generally considered to be a statement that has been proven based on previously established statements, such as other theorems, while a principle is more a fundamental truth or proposition that serves as the foundation for a system of belief or behavior in a broader sense. Although these terms are related to mathematical or scientific concepts, they do not accurately define a law or rule that is succinctly expressed as an equation like a formula does.