As long as the initial derivative reads f ' (c). For f ' (x) we must have c -> x.
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> In algebra, I tell students that it doesn't matter which point you label > (x1,y1) and which is (x2,y2) as long as you keep them consistent. All > your student has done is switch the points. I think it is perfectly fine. > c is still the "fixed point" x is still approaching it.