(x²-x+1/4)/(2(2x-1))=(x-1/2)²/4(x-1/2)=(x-1/2)/4 =(2x-1)/8 =1/4x-1/8
因为x²-x+1/4=1/4(4x²-4x+1)=1/4(2x-1)²所以(x²-x+1/4)/(2(2x-1))=1/4(2x-1)²/(2(2x-1))=1/8(2x-1)
（x-1/2）/4 =x/4-1/8
