1：去括号:-x+2(y-2)
=-x+2y-4
2a-3(b+c-d)
=2a-3b-3c+3d
1：a-(2a-2)
=a-2a+2
=-a+2
2:-(5x+y)-3(2x-3y)
=-5x-y-6x+9y
=-11x+8y