1. - (7x²-5x+3)-(7x²-5)=
2. - (3x+1)+(-3x²-3x+1)=
3. - (a+3b)+(3a-3b)=
4. - a²-5ab-b²-(a²+b²)=
5. - (x+y-z)-(x-y)+(x-y+z)=