a^7 + a^5 + 2a^2 + 28xy - 4y + 2x^2 - x = a^5(a^2 + 1) + 2(a^2 + 1) + 4(7xy - y + x^2 - x)= (a^5 + 2)(a^2 + 1) + 4(7xy - y + x^2 - x)= (a^5 + 2)(a^2 + 1) + 4(7xy - y) + 4(x^2 - x)= (a^5 + 2)(a^2 + 1) + 4y(7x - 1) + 4x(x - 1)= (a^5 + 2)(a^2 + 1) + 4y(7x - 1) + 4x(x - 1)
a^7 + a^5 + 2a^2 + 28xy - 4y + 2x^2 - x = a^5(a^2 + 1) + 2(a^2 + 1) + 4(7xy - y + x^2 - x)
= (a^5 + 2)(a^2 + 1) + 4(7xy - y + x^2 - x)
= (a^5 + 2)(a^2 + 1) + 4(7xy - y) + 4(x^2 - x)
= (a^5 + 2)(a^2 + 1) + 4y(7x - 1) + 4x(x - 1)
= (a^5 + 2)(a^2 + 1) + 4y(7x - 1) + 4x(x - 1)