1. (3x+1)+(-3x² -3x+1)=3x+1-3x² -3x+1=
=2-3x²
2. (a+3b)+(3a-3b)=a+3b+3a-3b=4а
3. a² -5ab-b² -(a² +b²)=a² -5ab-b² -a² -b²=
=-5аb-2b²
4. (x+y-z)-(x-y)+(x-y+z)=x+y-z-x+y+x-y+z=
=x+y
1. (3x+1)+(-3x² -3x+1)=3x+1-3x² -3x+1=
=2-3x²
2. (a+3b)+(3a-3b)=a+3b+3a-3b=4а
3. a² -5ab-b² -(a² +b²)=a² -5ab-b² -a² -b²=
=-5аb-2b²
4. (x+y-z)-(x-y)+(x-y+z)=x+y-z-x+y+x-y+z=
=x+y