# Why is it arsinh rather than arcsinh?

- Author:
- patrick.macmahon

Ever wondered why we say

**arcsin**for the inverse of the sine function, but**arsinh**for the inverse of the hyperbolic sine function? It's because arcsin gives the**arc**length on the unit circle for a given*y*-coordinate, whereas arsinh gives an**area**enclosed by a hyperbola and two rays from the origin for a given*y*-coordinate. The red shaded area below is equal to arsinh(*a*), where*a*is the length of the blue line segment.## New Resources

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