solve 2x^2+4x-7=0

Notice that this is a quadratic. First you should try factorisation, then if unsuccessful try completing the square (or the quadratic formula). In this example, factorisation is not possible (I can this further with demonstration.) So we must try Completing the square. Since the x^2 term has a '2' in front of it, we must get rid of this first, by taking it out as a factor. Then follow the give procedure for completing the square (I can show this further using the white board). If the student struggles with this approach I would consider letting them just use the quadratic formula - this would be a good way to check too.