This is in the subject content of an exam I plan to sit but I don't have my text book yet so I am working from free resources online, but I have never seen this before and I can't find anything like it by searching google, hopefully someone here can tell me where to find more info on this.
"Using quadratic theory (not calculus) to find the possible values of the function and the coordinates of the maximum or minimum points on the graph.
Eg for y = x2+2/x2-4x, if y = k then x2+2 =kx2 - 4kx,
Which has real roots if 16k2 + 8k - 8 >/= 0, ie if k </= -1 or k >/= 1/2; (Greater than or equals: >/=)
Stationary points are (1, -1) and (-2, 1/2)."