(1)6x²-2x-4x²+5x+1=(6x²-4x²)+(5x-2x)+1=(6-4)x²+(5-2)x+1=2x²+3x+1
(2)-ab³+3b³a=(-1+3)ab³=2ab³
(3)1/4x²y-3x²+3/4y²+2x²= 1/4x²y+(-3+2)x²+3/4y²
=1/4x²y-x²+3/4y²
（4）-3x²y+2x²y+3xy²-2xy² =(-3+2)x²y+(3-2)xy² =- x²y+xy²