1/2（x-1/2（x-1））-2/3（x-1）=1/2（x-1/2x+1/2）-2/3x+2/3=1/2（1/2x+1/2）-2/3x+2/3=1/4x+1/4-2/3x+2/3=-5/12x+11/12
