http://www-math.mit.edu/~djk/calculus_beginners/chapter03/section03.html http://www-math.mit.edu/~djk/calculus_beginners/chapter03/se... > if y = z + a * (x -

http://www-math.mit.edu/~djk/calculus_beginners/chapter03/section03.html http://www-math.mit.edu/~djk/calculus_beginners/chapter03/se... > if y = z + a * (x - z) then 1.) f(y) = f(x) + a * (f(x) - f(z)) This is incorrect, isn't it? It should be 2.) f(y) = f(z) + a * (f(x) - f(z)) if I'm not mistaken. For example, consider f(n) = n + 1 - z=1, x=2 - f(z)=2, f(x)=3 - f(z + a(x - z)) <=> f(1 + a); for a = -1, we should get f(0) = 1, Substituting into 1.) yields 3 + -1 * (3 - 2) = 2 (incorrect) Substituting into 2.) yields 2 + -1 * (3 - 2) = 1 (correct)