(1+x) y = 1-x => (y+1)x = 1-y => x = (1-y)/(1+y)
y(cx+d) = ax + b => (cy -a)x= b-dy => x = (b-dy)/(cy-a)
(2^x+1)y = 2^x => 2^x(1-y) = y => 2^x = y/(1-y) => x = ln[y/(1-y)]/ln2