Previous page : Hyperbolic functions – The cosinus hyperbolicus and its inverse

So if

and

then

The graph of this is seen below.

We can compare this with the exponential form of the sine function found here.

**The inverse function**

We get

The quadratic formula now gives us (with *a*=1, *b*= –2y and *c*= –1).

This gives us

So what sign to use? If we use the negative sign we get the log of a negative number, so we must have

The graph of this can be seen below.

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