CORE_MATH • SHS 1Term 2WAEC / WASSCE SyllabusVIP Lesson
Change of Subject of Formula
Transforming algebraic formulas, dealing with brackets, roots, powers, and variables appearing in multiple terms.
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Real-World Context & Relevance in Ghana
Electricians working with ECG power equations P = V²/R frequently rearrange the formula to find resistance R = V²/P or voltage V = √(PR) for safety checks.
Key Syllabus Learning Objectives
- 1Isolate target variables from linear, fractional, and radical formulas
- 2Handle formulas where the target variable appears on both sides of the equation
- 3Apply factoring techniques to isolate variables appearing in multiple terms
- 4Substitute numerical values into rearranged formulas accurately
1
Target Variable in Multiple Terms
When the target variable appears more than once, expand all brackets, collect all terms containing that variable on the left side, and move all other terms to the right side. Then factor out the target variable.
- Group all terms with the target variable on one side.
- Factor out the target variable: x(a + b) = c.
- Divide both sides by the cofactor: x = c / (a + b).
Core Takeaway:
Factoring is the key step whenever the target variable appears more than once.
WAEC / WASSCE Examiner Tips
- When squaring both sides to remove a root, square the ENTIRE side (e.g. if y = a + √x, you must first isolate √x = y - a before squaring!).
- Ensure the target variable is completely isolated on one side and does not appear on the other side.
- Never leave fractions within fractions in your final answer.
Common Candidate Pitfalls & Errors to Avoid
- Squaring individual terms instead of isolating the radical first: squaring a + √b is (a + √b)², not a² + b.
- Leaving the target variable on both sides of the equation.
- Sign errors when moving terms across the equals sign.
Topic Mastery Checklist
- Can I make r the subject in V = πr²h?
- Can I make x the subject in y = (2x + 1)/(x - 3)?
- Can I isolate t in T = 2π√(l/g)?
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