Factorising is the reverse of expanding — we take out a common factor.
For example $2x + 4 = 2(x + 2)$, because 2 divides both terms. And $x^2 + x = x(x + 1)$. Algebraic fractions can be simplified by dividing top and bottom, e.g. $\dfrac{4x}{2} = 2x$.
Remember
- Factorise by taking out the highest common factor.
- Check by expanding: $2(x+2) = 2x + 4$.