F (2x) = LNX, f (x) = lnx-ln2, how does the first step change into the second step!

F (2x) = LNX, f (x) = lnx-ln2, how does the first step change into the second step!

Let a = 2x
x=a/2
So f (a) = ln (A / 2) = lna-ln2
So f (x) = lnx-ln2