a / b 2x = c2 * d | * b 2x
a = c2 * d * b 2x | : ( c2 * d )
a / ( c2 * d ) = b 2x
ln ( a / ( c2 * d ) ) = 2x * ln(b) | : ( 2ln(b) )
ln ( a / ( c2 * d ) ) / ( 2ln(b) ) = x
A = R* ( I - a -x )
A/R = I - a-x
a-x = I - A/R
-x * ln(a) = ln( I - A/R )
x = - ln( I - A/R ) / ln(a)