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Well, try one of them.
function is continuous and differentiable from 1 to 3 (note not at zero)
f(3) = 3-1/3 = 8/3
f(1) = 0
[f(3)-f(1)]/(3-1) = 4/3
so where is the derivative 4/3?
f'(x) = 1 + 1/x^2
where does 1+1/x^2 = 4/3 ?
1/x^2 = 1/3
x = sqrt 3
yes, that is between x = 1 and x =3