（1）：-2X-3Y+5-7Y+3X-5
=(-2+3)X+(-3-7)Y+(5-5)
=X-10Y
（2）： 5X^3+2X^2Y+8X^3-4YX^2+3Y-1
=(5+8)X³+(2-4)X²Y+3Y-1
=13X³-2X²Y+3Y-1