整数的加减之先去括号,再合并同类项

1.(x-1）-(-2x)
=x-1+2x
=3x-1
2.-3(xy-2)+2(1-2xy)
=-3xy+6+2-4xy
=-7xy+8
3.(3x²-xy-2y²)-2(x²+xy-2y²)
=3x²-xy-2y²-2x²-2xy+4y²
=x²-3xy+2y²
4.3a-(2a-4b-6c)+3(-2c+2b)
=3a-2a+4b+6c-6c+6b
=a+10