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Inverse hyperbolic tangent
The inverse hyperbolic tangent is written with logarithms as
Area functions can be described with logarithms because all hyperbolic functions are defined by exponential functions.
Explanation
We start with the hyperbolic tangent to which applies
Substitution of eθ = k gives
We continue only with the positive solution and substitute k = eθ so that
Now we take the logarithm on both sides
Substitution of θ = artanh x gives
Example 1
You can see that tanh-1(0) = 0, because