Book 3 of the 5 essential Ordinary Level Leaving Cert books will introduce you to the concept of factors and teach you how to solve quadratic equations using factors.
Book 2 of the 5 essential Ordinary Level Leaving Cert book will teach you how to recognise and solve both the standard and substitution simultaneous equations.
Book 1 of the 5 essential books for Ordinary Level Leaving Cert will teach you how to recognise and solve two of the most important equations, the Straight Line Equation and the Quadratic Equation.