1、a-[b+(a+b)]
=a-b-(a+b)
=a-b-a-b
=-2b
2、-(5x+y)+(2x-3y)
=-5x-y+2x-3y
=(-5x+2x)+(-y-3y)
=-3x-4y
3、1/3a-(1/2a-4b-6c)+(-2c+2b)
=1/3a-1/2a+4b+6c-2c+2b
=(1/3a-1/2a)+(4b+2b)+(6c-2c)
=-1/6a+6b+4c