EDEXCEL GCSE FOUNDATION MATHS - What is Changing the Subject

Changing the Subject of an Equation

Changing the subject of an equation is like solving for a specific variable. It's like rearranging the equation to isolate that variable on one side of the equal sign. Here's a step-by-step guide:

1. Identify the Subject

• Subject: The variable you want to isolate.
• Equation: The mathematical expression you're working with.

2. Undo Operations

• Think of the equation as a set of instructions to calculate the subject.
• To isolate the subject, you need to reverse these instructions.
• Addition: Subtract the same value from both sides of the equation.
• Subtraction: Add the same value to both sides.
• Multiplication: Divide both sides by the same value.
• Division: Multiply both sides by the same value.

3. Simplify

• After applying each step, simplify the equation as much as possible.

Example:

Let's change the subject of the equation y = 2x + 5 to x.

1. Subject: x

2. Equation: y = 2x + 5

3. Step 1: Subtract 5 from both sides: y - 5 = 2x + 5 - 5

4. Step 2: Simplify: y - 5 = 2x
5. Step 3: Divide both sides by 2: (y - 5)/2 = 2x/2
6. Step 4: Simplify: (y - 5)/2 = x

Therefore, we've successfully changed the subject to x, and the new equation is x = (y - 5)/2.

Key Points:

• Remember to perform the same operation on both sides of the equation to keep it balanced.
• Always simplify the equation after each step.
• Practice with different examples to become comfortable with this technique.

Changing the subject of an equation is a fundamental skill in algebra, and it is essential for solving many mathematical problems. By mastering this technique, you will be able to manipulate equations to solve for any variable you need.