4.8x^8 y^7 - 12x^6 y^6 - 2.4x^6 y^5(2x^2 y^2 - 5y + 3)= 4.8x^8 y^7 - 12x^6 y^6 - 4.8x^8 y^5 (2x^2 y^2 - 5y + 3)= 4.8x^8 y^7 - 12x^6 y^6 - 9.6x^10 y^7 + 24x^8 y^6 - 14.4x^8 y^5= -9.6x^10 y^7 + 16x^8 y^6 - 14.4x^8 y^5 - 12x^6 y^6
4.8x^8 y^7 - 12x^6 y^6 - 2.4x^6 y^5(2x^2 y^2 - 5y + 3)
= 4.8x^8 y^7 - 12x^6 y^6 - 4.8x^8 y^5 (2x^2 y^2 - 5y + 3)
= 4.8x^8 y^7 - 12x^6 y^6 - 9.6x^10 y^7 + 24x^8 y^6 - 14.4x^8 y^5
= -9.6x^10 y^7 + 16x^8 y^6 - 14.4x^8 y^5 - 12x^6 y^6