(x? +5)/2=(x? -3+8)×5/5/2=(x? -3+8)/5×(5/2)=(x? -3)/5+8/5×(5/2)=(x? -3)/5+4
In short, the purpose is to make "the part after 1+ in brackets" and "the index outside brackets" into reciprocal forms.
I sent you pictures and words. I don't know if you can understand them.