25(x-y)²-9(x+y)²=[5(x-y)+3(x+y)][5(x-y)-3(x+y)]=[5x-5y+3x+3y][5x-5y-3x-3y]=(8x-2y)(2x-8y)2a²x-2ax+1/2x=x(4a²-4a+1)/2=x(2a-1)²/2