①-（x+y）+（3x-7y）
=-x-y+3x-7y=2x-8y
②2a+2（a+1）-3（a-1）
=2a+2a+2-3a+3=a+5
③4a^2-3a+3-3(-a^3+2a^2+1)
=4a^2-3a+3+3a^3-6a^2-3
=3a^3-2a^2-3a
=a(3a^2-2a-3)