Đáp án:
`( a^4 + a^3b + a^2b^2 + ab^3 + b^4) (a-b)`
` = a^5 - a^4b + a^4b - a^3b^2 + a^3b^2 - a^2b^3 + a^2b^3 - ab^4 + ab^4 - b^5`
` = (a^5 - b^5) - (a^4b - a^4b) - (a^3b^2 - a^3b^2) - (a^2b^3 - a^2b^3) - (ab^4 - ab^4)`
` = a^5 - b^5 -0-0-0-0`
` = a^5 - b^5`