(7z³+2z²-2z-5)-(6z³-z²+2z)=3z²-(6z-z³)​

z=2, 5

7z^3+2z^2-2z-5-6z^3+z^2-2z=3z^2-6z+z^3

z^3+3z^2-4z-5=3z^2-6z+z^3

-4z-5=-6z

-4z+6z=5

2z=5

z=2,5