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Inverse hyperbolic cosine
The inverse hyperbolic cosine can be expresses with logarithms as
Explanation
We start with the hyperbolic cosine
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
After substitution of θ = arccosh x we get
Example 1
You can see that cosh−1(1) = 0, because
cosh−1(1) = ln (1 + √0) = ln (1) = 0