When should I use the quadratic formula?

If you're asked to solve a quadratic equation, you could factorise it, or you could use the quadratic formula. The quickest way is to factorise, but sometimes the numbers are too tricky to factorise, (if an exam question asks for the answer in decimal places, this is a good indication you will need this method) so in these situations we use the quadratic formula:

x= (-b+/-sqrt(b²-4ac))/2a

given the equation ax^​2​+bx+c=0

You can then substitute the numbers from your equation into the formula, and you will get two values of x (remeber to do both + and - the square root) just like you would if you were to factorise the equation.