Rearranging Formulae

Summary and Exam Tips for Rearranging Formulae

Rearranging Formulae is a subtopic of Equations, Formulae and Identities, which falls under the subject Mathematics in the Edexcel IGCSE curriculum. Understanding how to rearrange formulae is crucial for solving algebraic equations and making specific variables the subject. The subject of a formula is the variable that stands alone on one side of the equation. To make a variable, such as $x$, the subject, you need to rearrange the equation so that $x$ is isolated. This involves performing operations like cross multiplication, moving terms, and using inverse operations to isolate the desired variable. For example, in the formula $A = b \times h$, $A$ is the subject. When making $y$ the subject, remember to consider both positive and negative solutions after square rooting. Practice questions often involve making different variables the subject, such as rearranging a formula to make $l$ the subject in the context of pendulum length. By treating the formula as an equation and using inverse operators, you can effectively change the subject of any formula.

Exam Tips

• Understand the Subject: Always identify the current subject of the formula and the variable you need to isolate.
• Order of Operations: Follow the correct order of operations when rearranging formulae. This often involves reversing operations like addition, subtraction, multiplication, and division.
• Inverse Operations: Use inverse operations to isolate the variable. For example, if a variable is multiplied, divide to isolate it.
• Practice: Work through past paper questions to familiarize yourself with different types of rearranging problems.
• Check Your Work: After rearranging, substitute values to ensure the formula works correctly with the new subject.