fn-gn=12⁢π⁢ⅈ⁢∫|z|=rf⁡(z)-g⁡(z)zn+1⁢ⅆ⁡z=12⁢π⁢rn⁢∫02⁢π(f⁡(r⁢ⅇⅈ⁢θ)-g⁡(r⁢ⅇⅈ⁢θ))⁢ⅇ-n⁢ⅈ⁢θ⁢ⅆ⁡θ.