- #1

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The mass discrepancy, defined as the ratio of the gradients of the total to baryonic gravitational potential, can be described by a simple function of centripetal acceleration:

##D(x) = \frac{\Phi'}{\Phi'_{b}} ##

Where ##x = a/a0## and ##D(x)## is the inverse of the following equation:

##\mu(x) = \frac{x}{\sqrt{1+x^2}}##

It's not clear to me how ##D(x)## is the inverse of the equation ##\mu(x) = \frac{x}{\sqrt{1+x^2}}##.

For example, how would one substitute ##\mu(x)## for ##D(x)##?