Gain of the amplifier
If we have open loop gain of 2dB or 3dB what happens if we use this in
  closed loop




Rearranging... Y = G(X - Y) therefore Y(1 + G) = G.X

So \$\dfrac{Y}{X} = \dfrac{G}{1+G}\$

If G is 2 dB (1.26 in real numbers), the net gain is 0.558.

If G was large, the net gain would be close to unity.