This is a useful worksheet which explains what the discriminant is and how it's value determines the roots of an equation. There is then an exercise for students to try. This would make a useful homework task which students could go away and try, or you could use this as a set of notes and some questions to do in class. Phildb has shared a lot of similar resources for A-level, these could be complied into a useful set of revision notes and exercises for your students. Thank you for sharing.