Im trying to figure out how the author of this ( The Sallen-Key filters (hmc.edu) ) (the very first/top problem)came to the conclusion Va = Vout((Z2+Z4)/Z2)).I was able to come up with same exact node analysis equations,but trying to solve them I get different results.

So: Va-Vout = Vout(Z2/Z4) -----> Va = Vout((Z2+Z4)/Z2)) I would just like to know how they got to this

My: Va = Vout(Z2/Z4) + Vout and simplified version : Va = Vout[(Z2/Z4) + 1]

Im sure im just overthinking this,but any help is appreciated.