9 ) Black's Rook Pins the King , So Black will do sacrifice from its Knight, if Rook or pawn captures then black loses material and loses game quickly because dXc4 immediately check on the King and loses materials. Black will have more pawns and easy to win game. So exchanging piece is not good always. first see the position of the game then decide exchanging piece better for your game?
So here better move for white is Rd1.
37...Nc4 38.Rxc4 dxc4+ 39.Kc3 Rd3+ 40.Rxd3 cxd3
37...Nc4 38.bxc4 dxc4+ 39.Kxe4 Rxd2 40.Rxc4 Kg6 41.Rc6+ Kh5 42.Kf3 Rxa2 43.Rc3 Rb2 44.Rc7 Rb3+ 45.Kf2 Rxb5 46.Rxa7 Rb2+ 47.Kf3 b5
Better move is 37...Nc4 38.Rd1 Kg6