Consider the difference of polynomials [tex](7x^8 + 8x^6 - 2x + 9) - (4x^8 + 3x^7 + 3).[/tex]
The first thing you have to do is take that "minus" sign through the parentheses containing the second polynomial (just change sign + to - and sign - to +):
[tex](7x^8 + 8x^6 - 2x + 9) - (4x^8 + 3x^7 + 3)=7x^8+8x^6-2x+9-4x^8-3x^7-3.[/tex]
Then combine terms with the same degree:
[tex]7x^8+8x^6-2x+9-4x^8-3x^7-3=(7x^8-4x^8)-3x^7+8x^6-2x+(9-3).[/tex]
Note that
[tex]7x^8-4x^8=(7-4)x^8=3x^8,\\ \\9-3=6.[/tex]
Thus,
[tex](7x^8 + 8x^6 - 2x + 9) - (4x^8 + 3x^7 + 3)=3x^8-3x^7+8x^6-2x+6.[/tex]
