Expressions and Formulae

Summary and Exam Tips for Expressions and Formulae

Expressions and Formulae is a subtopic of Equations, Formulae and Identities, which falls under the subject Mathematics in the Edexcel IGCSE curriculum. This section focuses on substitution and the rearrangement of formulae. Substitution involves replacing the unknown variable with a given value and performing calculations based on the order of operations. For example, to find the value of $3m - 5$ when $m = 6$, substitute and compute: $3 \times 6 - 5 = 13$. Similarly, evaluate expressions like $3x + 4y$ by substituting $x = 10$ and $y = 2$ to get $38$.

Rearranging formulae involves making a specific variable the subject, meaning it stands alone on one side of the equation. For instance, in the formula $A = b \times h$, $A$ is the subject. To make another variable the subject, techniques like cross-multiplication or factoring are used. When dealing with equations involving squares, remember to consider both positive and negative roots. For example, to make $y$ the subject in $m(y + n) = n(n - y)$, rearrange and factor to solve for $y$.

Exam Tips

• Understand Substitution: Practice substituting values into expressions and ensure you follow the order of operations (PEMDAS/BODMAS).

• Rearrange Formulae: Familiarize yourself with techniques like cross-multiplication and factoring to make a variable the subject of a formula.

• Check Your Work: After rearranging or substituting, always double-check your calculations to avoid simple errors.

• Consider All Solutions: When dealing with squares, remember to include both positive and negative solutions.

• Practice Regularly: Consistent practice with a variety of problems will help reinforce these concepts and improve your problem-solving skills.