1. The problem is to factorise an algebraic expression. Since no specific expression was given, let's consider a general example: factorise $x^2 - 5x + 6$. 2. The formula used for factorising quadratic expressions of the form $ax^2 + bx + c$ is to find two numbers that multiply to $ac$ and add to $b$. 3. For $x^2 - 5x + 6$, $a=1$, $b=-5$, and $c=6$. We need two numbers that multiply to $1 \times 6 = 6$ and add to $-5$. 4. The numbers are $-2$ and $-3$ because $-2 \times -3 = 6$ and $-2 + -3 = -5$. 5. Rewrite the middle term using these numbers: $x^2 - 2x - 3x + 6$. 6. Factor by grouping: $x(x - 2) - 3(x - 2)$. 7. Factor out the common binomial: $(x - 3)(x - 2)$. 8. Therefore, the factorised form of $x^2 - 5x + 6$ is $$(x - 3)(x - 2)$$. This method can be applied to other quadratic expressions to factorise them.