f(x) = e^{1/x}
f'(x) = [1/x]' * e^{1/x}
f'(x) = [x^-1]' * e^{1/x}
f'(x) = -x^-2 * e^{1/x}
f'(x) = -e^{1/x}/x^2
Nun schauen wir uns mal deine Funktion an
f(x) = x * e^{1/x}
f'(x) = 1 * e^{1/x} + x * (-e^{1/x}/x^2)
f'(x) = 1 * e^{1/x} - e^{1/x}/x
f'(x) = e^{1/x} * 1 - e^{1/x} * 1/x
f'(x) = e^{1/x} * (1 - 1/x)