This key facts covers Key Features of Direct Proportion within Direct Proportion for GCSE Mathematics. Revise Direct Proportion in Ratio & Proportion for GCSE Mathematics with 15 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 2 of 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Key Features of Direct Proportion
We write y ∝ x to mean "y is directly proportional to x"
This means y = kx where k is a constant
| Feature | What it means |
|---|---|
| Graph shape | Straight line through the origin (0,0) |
| When x doubles | y also doubles |
| Ratio y/x | Always the same (equals k) |
| The constant k | k = y ÷ x (the gradient of the line) |
Practice questions for Direct Proportion
Which of the following correctly reads the mathematical statement y ∝ x?
Explain what it means for y to be directly proportional to x. Your answer should refer to the equation and the graph.