The correct proof process is as follows: because 1/3

Let a small positive number ε be │ f (x1)-f (x2) │ = │1/x/kloc-0 │ = │ x1-x2 │/(x1x2). ε, because │ x1-x2 │/(x1x2) < = 9 │ x1-x2 │.

Just 9 │ x 1-x2 │

Take δ=ε/9, then when │ x 1-x2