SOLUTION: factorize 3a^3b-243ab^3 this is my assignment question but i have no idea how to answer it i dont understnd the question

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Question 151907: factorize 3a^3b-243ab^3 this is my assignment question but i have no idea how to answer it i dont understnd the question
Answer by orca(409) About Me  (Show Source):
You can put this solution on YOUR website!
First factoring out the factor that are common to both terms.
3a^3b-243ab^3
= 3a^3b - 3*81ab^3
= (3ab)*a^2 - (3ab)*81b^2
= 3ab(a^2 - 81b^2)
= 3ab[a^2 - (9b)^2]
= 3ab(a + 9b)(a - 9b)