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**Kandai****Guest**

I know how to get from here:

-2(w-5)(w+5)(w^2+25)

to here:

-2w^4+1250

But I don't know how to get from here:

-2w^4+1250

to here:

-2(w-5)(w+5)(w^2+25)

The same with this problem:

a^9-1

(a-1)(a^2+a+1)(a^6+a^3+1)

**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 21,470

Its always difficult to find the factors, given the simplest form.

a^3 - b^3 is (a-b)(a^2 + ab + b^2).

If one of the factors is known, it becomes a bit easier.

For lower degrees, by remembering some formulae, it can be done easily.

Like a^2 - b^2 = (a+b) x (a-b),

(a^3 + b^3) = (a+b) x (a^2 - ab + b^2) etc.

When you are aksed to prove that the LHS is equal to the RHS,

it is always better to start with lower degrees.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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