Thread: Factoring By Grouping..

errr.. didnt know where to put this but im reviewing for my calculus exam and this is the first unit
2x^4-10x^3-x^2+5x

help.

Originally Posted by Arbitur

errr.. didnt know where to put this but im reviewing for my calculus exam and this is the first unit
2x^4-10x^3-x^2+5x

help.

I don't know what you mean by factoring by grouping, but to factor this
we start by taking out the so:



Now we observe that this is high-school maths, so if this
is factorisable the the factors will have integer numeric terms.
Now is prime so that suggests we consider
factors of the form , for or .

The first one we try is , putting
in the expression gives zero and so is a factor.

Then doing the divisions gives us:

.

RonL

Originally Posted by Arbitur

errr.. didnt know where to put this but im reviewing for my calculus exam and this is the first unit
2x^4-10x^3-x^2+5x

help.

2x^4 -10x^3 -x^2 +5x
= (2x^4 -10x^3) -(x^2 -5x)
= (2x^3)(x -5) -x(x -5)
= (x-5)(2x^3 -x)
= (x-5)(2x^2 -1)(x)
= x(x-5)(2x^2 -1) -----------answer.

First I'll repeat CaptainBlack's first step: Factor out an "x":



Now look at the cubic factor. I'll regroup (hence "factoring by grouping&quot this as:



We can factor an x from the first pair of terms and a -5 from the second pair giving:



Notice that we can now factor a common from both terms. So:



So

Finally, putting the now factored cubic term back into the original problem we get:



just as CaptainBlack had. Usually in factoring by grouping we leave the quadratic factors alone if they don't factor over the integers, so I'll end the factorization here.

-Dan
(Apologies to ticbol. I didn't see your post on the thread before I wrote this.)

Hi:

Factoring GCF x from the initial expression gives 2x^4-10x^3-x^2+5x = x(2x^3 -10x^2 - x + 5). Now taking 2x^2 from the first two terms within parentheses gives x[(2x^2)(x-5) - x + 5] or, x[(2x^2)(x-5) - (x-5)]. Finally, we factor out the (x-5) common to both terms within brackets leaving x[(x-5)(2x^2 - 1)] or simply x(x-5)(2x^2 - 1).

Regards,

Rich B.

Originally Posted by topsquark

(Apologies to ticbol. I didn't see your post on the thread before I wrote this.)

No need to apologize.

Yeah, same problem here. I also do not like to "repeat" another guy's solution that is why I avoid answering sometimes. So happens that after I post my reply, there is/are already posted replies to the same question. :-)
Some guys can type faster than my right pointing finger.

Me, who hates hints, never mind complete solutions, to solve a problem?

If a problem says, "here is a clue" or "Hint:", I will ignore that problem 99.99045 percent.

That is why also I like going home and finding most of the recent questions already answered. Then I can answer the ones left untouched----if I can solve them. :-).
No need to pump this here harassed lone finger typer.

But, if I see that posted answers are not to my liking, or if I can give another way, I will post another, different, answer.