a. 8t^3 + 64
= (2t)^3 + 4^3 (HĐT 6)
= (2t+4)(4t^2-8t+16)
b.(3x^3 + 4xy)^3 (HĐT 4)
= (3x^3)^3 + 3.(3x^3)^2.4xy - 3.3x^3.(4xy)^2 + (4xy)^2
= 27x^9 + 108x^7.y - 144x^5.y^2 + 16.x^2.y^2
c. (3x^2-5xy^3).(3x^2+5xy^3) (HĐT 3)
= (3x^2)^2-(5xy^3)^2
= 9x^4-25.x^2.y^6