25a^2 - (a+3)^2 = 25a^2 - (a^2 + 6a + 9)= 25a^2 - a^2 - 6a - 9= 24a^2 - 6a - 9
16^4 - 81 = 65536 - 81= 65455
27m^3 + n^3 = 27m^3 + n^3
a^2 - b - a^2 - b = -2b
25a^2 - (a+3)^2 = 25a^2 - (a^2 + 6a + 9)
= 25a^2 - a^2 - 6a - 9
= 24a^2 - 6a - 9
16^4 - 81 = 65536 - 81
= 65455
27m^3 + n^3 = 27m^3 + n^3
a^2 - b - a^2 - b = -2b