Factorising quadratic expressions

A quadratic expression has an x^2 term as its highest power, such as x^2 + 7x + 12. Factorising means rewriting it as a product of simpler pieces, like (x + 3)(x + 4). This matters because a product is easy to work with: if two brackets multiply to zero, one of them must be zero. That is how many quadratic equations are solved.