This key facts covers Key Facts within Proportion Graphs for GCSE Mathematics. Revise Proportion Graphs in Ratio & Proportion for GCSE Mathematics with 14 exam-style questions and 4 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 2 of 6 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Key Facts
| Symbol | y ∝ x means "y is directly proportional to x" |
| Formula | y = kx, where k is the constant of proportionality |
| Graph | A straight line through the origin (0,0) |
| Key Feature | y/x always equals the same value (k) |
| Higher: y ∝ x² | y = kx² (quadrupling x means y × 4²) |
Practice questions for Proportion Graphs
Which of the following describes the graph of a direct proportion relationship?
Aisha says: 'Because the graph of y against x is a straight line, y must be directly proportional to x.' Is Aisha correct? Explain your answer.
Quick recall flashcards
Direct vs Inverse
Direct: both increase together (y ∝ x). Inverse: one increases, other decreases (y ∝ 1/x).
Finding k
Use given values to find constant k, then apply to new values