Input and output resistance of an opamp circuit
I would like to know what the input and output resistances in opamp circuits represent and if possible how to obtain them from equations

I assume you are asking for "theortical" formulas, right? OK - from system theory we derive the following expressions for the whole circuit; all opamp resistances without feedback will be drastically altered due to feedback (Loop Gain LG):

1.) Non-inv. input: r,p=rp,o*(1+LG)

2.) inv. input:     r,i=rn,o/(1+LG)

3.) input R2:       r,2=R2+r,i (very close to R2)

4.) output:         r,out=r,o/(1+LG)

rp,o and rn,o: dynamic input resistances without feedback;

r,o: dyn. output resistance without feedback;

Loop Gain: LG=Aol*feedback factor=AoR2/(R1+R2). 

PS: Your measurement of r,out is OK (in principle). However, I suggest (a) to use a smaller external resitor (R3=1...5 Ohms) to realize a suitable voltage divider (together with r,out) or (b) to use a much larger resistor for realizing a "good" current source (current practically determined by R3 only).