Quadratics
Lesson 1 of 14
Solving quadratics by factorising
Objective. Solve x² + bx + c = 0 by factorising into two brackets.
The key idea
Find two numbers that multiply to give c and add to give b. If a product is zero, at least one factor must be zero.
Worked example
Solve x² + 2x − 15 = 0.
- 1Two numbers multiplying to −15 and adding to 2 are 5 and −3.
- 2(x + 5)(x − 3) = 0.
- 3So x + 5 = 0 or x − 3 = 0.
Answer: x = −5 or x = 3
Practice
Each question comes with a picture and a listen button. Try it first, then reveal the answer.
Common mistake. Forgetting the negative root when square rooting.
Your progress
Tick each step as you finish it — Continue brings you back here.
0 of 5 steps complete