Use the Product Rule: x^a x^b = x^a + b
5m^3 + 1 n^2 - 7m^2n + n + mn^2 - n^3 - (mn^2 + 2m^3)
Simplify 3 + 1 to 4
5m^4 n^2 - 7m^2n + n + mn^2 - n^3 (mn^2 + 2m^3)
Simplify brackets
5m^4 n^2 - 7m^2n + n + mn^2 - n^3 - mn^2 - 2m^3
Collect like terms
5m^4 n^2 - 7m^2n + n + n + (mn^2 - mn^2) - n^3 - 2m^3
Simplify
5m^4n^2 - 7m^2n + n - n^3 - 2m^3
