This study notes covers Worked Example 5: Square Relationships within Proportion for GCSE Mathematics. Revise Proportion in Number for GCSE Mathematics with 12 exam-style questions and 22 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 11 of 15 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 11 of 15
Practice
12 questions
Recall
22 flashcards
Worked Example 5: Square Relationships
y is directly proportional to x². When x = 3, y = 18. Find y when x = 5.
Solution
y ∝ x², so y = kx²
When x = 3, y = 18: 18 = k × 3²
18 = k × 9
k = 18 ÷ 9 = 2
So y = 2x²
When x = 5: y = 2 × 5² = 2 × 25 = 50
Answer: y = 50