Derivatives of power function on ℂ, ℝ, ℝ≥0, and ℝ≥0∞ #
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We also prove differentiability and provide derivatives for the power functions x ^ y.
Although λ x, x ^ r for fixed r is not complex-differentiable along the negative real
line, it is still real-differentiable, and the derivative is what one would formally expect.
This lemma says that λ x, a ^ x is strictly differentiable for a < 0. Note that these
values of a are outside of the "official" domain of a ^ x, and we may redefine a ^ x
for negative a if some other definition will be more convenient.
The function (1 + t/x) ^ x tends to exp t at +∞.
The function (1 + t/x) ^ x tends to exp t at +∞ for naturals x.