This study notes covers Worked Example: Quadratic - Negative Constant within Factorising for GCSE Mathematics. Revise Factorising in Algebra for GCSE Mathematics with 12 exam-style questions and 3 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 13 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
Worked Example: Quadratic - Negative Constant
Factorise: x² + 2x - 15
Step 1 Set up the problem
Need: multiply to -15, add to +2
Negative product means ONE negative, ONE positive
Step 2 Find the right pair
-3 × 5 = -15, -3 + 5 = +2 ✓
Final Write the brackets
x² + 2x - 15 = (x - 3)(x + 5)
Practice questions for Factorising
Which is the correct factorisation of 6x + 15?
A student factorises x² + 5x + 4 as (x + 4)(x + 4). Explain why this is incorrect and give the correct factorisation.