(10x^4 - 4x^3 - 7x^2 + 5x + 9) - (2x^4 - 5x^3 - 4x^2 + 9x + 3)
first, rearrange the terms :
(10x^4 - 2x^4 - 4x^3 + 5x^3 - 7x^2 + 4x^2 + 5x - 9x + 9 - 3)
keep in mind that only x-terms with the same power can have an effect on each other hence the difference will be :
8x^4 - x^3 - 3x^2 - 4x + 6
