Year 9 - Maths
Evaluating expressions with and without changing the subject
Expressions and formulae
Study Hub
Study Guides
This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit develops pupil understanding of formulae and how to rearrange them. Pupils will learn how to recognise and manipulate binomials and learn to recognise the difference of two squares.
Lesson Summary
You will learn to evaluate an expression where the subject has been changed and where it has not.
Key Notes
- Changing the subject can make it easier to evaluate a formula.
- It is possible to evaluate a formula without changing the subject.
- Both forms of the formula give the same result.
Vocabulary To Learn
- Subject of an equation/formula: The subject of an equation/a formula is a variable that is expressed in terms of other variables. It should have an exponent of 1 and a coefficient of 1.
Common Mistakes To Avoid
- Changing the subject of an equation or formula is only done when you are told to.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Changing the subject can make it easier to evaluate a formula. It is possible to evaluate a formula without changing the subject.
2. Use this key word in a maths sentence and explain it clearly. 'Subject of an equation/formula'
The subject of an equation/a formula is a variable that is expressed in terms of other variables. It should have an exponent of 1 and a coefficient of 1. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Changing the subject of an equation or formula is only done when you are told to. Correction: Having students practise rearranging before substituting and vice versa allows them to decide when the skill could be useful.
More Lessons In This Unit
- Additive relationships Study Guide
- Changing the subject to suit the context Study Guide
- Changing the subject with more complex formula Study Guide
- Changing the subject with simple formula Study Guide
- Checking and securing solving linear equations Study Guide
- Checking and securing understanding of the distributive law with algebraic terms Study Guide
- Difference of two squares Study Guide
- More complex binomial products Study Guide
- Multiplicative relationships between terms Study Guide
- Problem solving with expressions and formulae Study Guide
- The product of two binomials Study Guide
Browse all guides in the Year 9 Maths guide library.