I am sposed to find a binomial factor for y^9-125, but I got confused and stumped. I tried to plug it in to a website to see if it would help, but it said the problem was unfactorable. Help..?

Question

anonymous · Answer

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hero · Answer

This is the difference of cubes. It is factorable

anonymous · Answer

Then how do I factor it, because I'm confused.

hero · Answer

(a+b)(a^2 -ab +b^2)

hero · Answer

a = y^3
b = 5

(y^3-5)(y^6 + 5y^3+25)

anonymous · Answer

Yes, I know, but I can't figure it out

hero · Answer

You just have to memorize the formula: 

The cube root of y^9 = y^3
The cube root of 125 = 5

Therefore a = y^3, b = 125

and a^2 = y^6    (because y^3 squared equals y^6)
and b^2 = 25     (because 5^2 = 25)

anonymous · Answer

I got y^3-5.. is that correct?

anonymous · Answer

Nvm, thanks :3

hero · Answer

Yes, I already provided the solution as you saw above.

anonymous · Answer

http://www.wolframalpha.com/input/?i=y^9-125 I notice the question says "factor" not "find a binomial factor of"

anonymous · Answer

I wasn't paying attention to that, just the method :) Thanks

anonymous · Answer

estudier: i think you're the one who gave me that link also in one of the question i asked and it really helped me a lot. THANKS