1.(-2a)³·b²÷(8a³b²)
2.-5x(2x²-3x+4)+4x³+15x
3.(x²-2y²)(x+2y)-2xy(x-y)
4.(x-y+z)(x-y-z)
化简求值
[(x+y)(x-y)-(x+y)²-2y(x-2y)]÷(-2y),其中x=5,y=2003