(10x^3 - 5y^2)(10x^3 + 5y^2)= 10x^3 10x^3 + 10x^3 5y^2 - 5y^2 10x^3 - 5y^2 5y^2= 100x^6 + 50x^3y^2 - 50x^3y^2 - 25y^4= 100x^6 - 25y^4
(10x^3 - 5y^2)(10x^3 + 5y^2)
= 10x^3 10x^3 + 10x^3 5y^2 - 5y^2 10x^3 - 5y^2 5y^2
= 100x^6 + 50x^3y^2 - 50x^3y^2 - 25y^4
= 100x^6 - 25y^4