b/ $(a-b)^4\\=[a+(-b)^4]\\=a^4+4a^3.(-b)+6a^2(-b)^2+4a(-b)^3+(-b)^4\\=a^4-4a^3b+6a^2b^2-4ab^3+b^4$
Vậy $(a-b)^4=a^4-4a^3b+6a^2b^2-4ab^3+b^4$
$(a-b)^5\\=[a+(-b)]^5\\=a^5+5a^4(-b)+10a^3(-b)^2+10a^2(-b)^3+5a(-b)^4+(-b)^5\\=a^5-5a^4b+10a^3b^2-10a^2b^3+5ab^4-b^5$
Vậy $(a-b)^5=a^5-5a^4b+10a^3b^2-10a^2b^3+5ab^4-b^5$
$(a+1)^4\\=a^4+4a^3.1+6a^2.1^2+4a.1^3+1^4\\=a^4+4a^3+6a^2.1+4a.1+1\\=a^4+4a^3+6a^2+4a+1$
Vậy $(a+1)^4=a^4+4a^3+6a^2+4a+1$
$(a-1)^5\\=[a+(-1)]^5\\=a^5+5a^4.(-1)+10a^3.(-1)^2+10a^2.(-1)^3+5a.(-1)^4+(-1)^5\\=a^5-5a^4+10a^3.1-10a^2.1+5a.1-1^5\\=a^5-5a^4+10a^3-10a^2+5a-1$
Vậy $(a-1)^5=a^5-5a^4+10a^3-10a^2+5a-1$