(5xy – 2yz – 2zx + 10xyz) – (3xy + 5yz – 7zx)= 5xy – 2yz – 2zx + 10xyz – 3xy – 5yz + 7zx=5xy – 3xy – 2yz – 5yz – 2zx + 7zx + 10xyz= 2xy – 7yz + 5zx + 10xyz