Maths Literacy Matric Revision: Changing the subject of a formula

Revision Notes: Changing the Subject of a Formula


Changing the subject of a formula is a fundamental algebraic skill essential for solving equations and manipulating mathematical expressions. This ability is crucial in various fields of mathematics and its applications, making it a critical component of the Mathematical Literacy curriculum for Grade 12. Understanding how to change the subject of a formula allows students to isolate a variable in an equation, facilitating problem-solving and analysis in diverse contexts such as physics, chemistry, finance, and everyday problems.

Key Points

  1. Definition: Changing the subject of a formula means rearranging the formula to make a different variable the subject or the isolated term on one side of the equation.
  2. Basic Steps:
  3. Identify the term you need to isolate (new subject).
  4. Use inverse operations to systematically isolate the desired variable.
  5. Apply algebraic operations equally to both sides of the equation to maintain equality.
  6. Common Operations:
  7. Addition and subtraction
  8. Multiplication and division
  9. Using reciprocals for fractions
  10. Applying roots (square roots, cube roots, etc.)
  11. Exponents

Real-World Applications

Example 1: Geometry – Area of a Triangle

Formula: ( A = \frac{1}{2} \times base \times height )
– To make ‘height’ the subject:
A = \frac{1}{2} \times base \times height \
2A = base \times height \
height = \frac{2A}{base}

Example 2: Finance – Simple Interest

Formula: ( I = P \times R \times T )
– To find Principal ‘P’:
I = P \times R \times T \
P = \frac{I}{R \times T}

Common Misconceptions and Errors

  1. Neglecting Inverse Operations: Forgetting to apply the correct inverse operation can lead to incorrect isolation of the variable.
  2. Not Keeping Balance: Failing to apply operations equally to both sides of the equation can invalidate the equality.
  3. Mismanagement of Terms: Misplacing or mishandling terms while performing operations can lead to incorrect formulas.

Strategies to Avoid Errors:

  • Always perform the same operation on both sides of the equation.
  • Check each step by substituting values back into the original equation if possible.
  • Practice rearranging different types of formulas to become familiar with a variety of algebraic manipulations.

Practice and Review

Practice Problems:

  1. Rearrange the formula to make ‘b’ the subject: ( a = \frac{c}{b} )
  2. Change the subject to ‘r’: ( I = P \times R \times T )
  3. Make ‘l’ the subject of the formula: ( A = l \times w )


  1. ( a = \frac{c}{b} )
    a \times b = c \
    b = \frac{c}{a}
  2. ( I = P \times R \times T )
    P = \frac{I}{R \times T}
  3. ( A = l \times w )
    l = \frac{A}{w}

Examination Tips:

  • Look for keywords in the question asking for “change,” “rearrange,” or “make _ the subject.”
  • Write out each algebraic step to minimize errors.
  • Manage your time efficiently, ensuring you attempt each type of problem.

Connections and Extensions

  • Link to Other Topics: Changing the subject of a formula is related to solving linear equations, proportions, and working with functions.
  • Interdisciplinary Links: This skill is used in physical sciences for formulas in physics and chemistry, and in financial mathematics for computing interests and loans.

Summary and Quick Review

  1. Changing the subject involves isolating a different variable in an equation.
  2. Use inverse operations systematically and maintain equation balance.
  3. This skill is applicable in multiple real-world scenarios and other subject areas.

Additional Resources

  • Online Videos: Khan Academy and YouTube tutorials on algebraic manipulation and changing the subject of a formula.
  • Educational Platforms: Websites such as Coursera, EdX, and FutureLearn offer courses that touch on algebraic skills.
  • Books: Algebra textbooks and Mathematical Literacy workbooks that provide additional practice problems and explanations.

By mastering this skill, you will enhance your ability to solve complex problems efficiently, a vital competency in both academic and real-world settings. For more detailed examples and exercises, refer to reliable sources like textbooks and online educational platforms.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.