Solve the quadratic equation (x^2)-x-12=0 (easy), (x^2)-9=0 (special case), (x^2)+5x-13=0 (quadratic formula)

For each of the above the methodology is fairly similar, first try and do it just by looking at it then try the quadratic formula if that doesn't work. At GCSE level I don't think there's any need to worry about the discriminant equaling zero or a negative number but if it comes up that could be taught as well.Solutions:(x^2)-x-12=0: x= -3 or 4(x^2)-9=0: x= -3 or 3(x^2)+5x-13: a=1 b=5 c=-13 --> quadratic formula used to produce an answer in surd form and is then simplified if possible.