This is for an ideal opamp which its VCC pin is connected to some positive voltage(15V) and its VEE pin is connected to some negative voltage(-15V).
The equation of Vout=-Vin*Rf/Rin
When working with microcontroller the lowest voltage is GND.
If we connect the VEE pin of the opamp to GND the equation of Vout can't be the same because the lowest possible voltage is GND. Which is the equation for the new 'state' of the opamp?