If open-loop gain is Aod = 999 in the circuit of the closed-loop

From given circuit
V– = V_o
V+ = V_i

A_od =	V_o	=	V_o
	V₊ – V_–		V_i – V_o

999 =	V_o
	V_i – V_o

999 V_i – 999 V_o = V_o
999 V_i = 1000 V_o

or	V_o	=	999	= 0.999
	V_i		1000

or A_CL =	V_o	= 0.999
	V_i