factoring: having trouble with 2x^2 + 2w - 15

jdruopp

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Apr 27, 2007
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I am having trouble factoring this:

2x^2 + 2w - 15

Shouldnt the factors be 5 and 3?
But i come up with 2w^2 -x -15 OR 2w^2 +x -15

What am I doing wrong?
 
Re: factoring

jdruopp said:
Shouldnt the factors be 5 and 3?
That may be the strangest thing I ever have heard. The factors should be what they are. You cannot just assume them and become distressed at your assumptions.

Factoring requires a little logical thinking. Don't panic.

When presented with this problem, i would simply write down most of the solution. There is only one way to factor the '2', so:

(2x __ _____)(x __ _____)

Trying to fill in the blanks,

The factors of 15 are 1 & 15 or 3 & 5. That's it. 15 is negative, we'll need opposite signs.

2*1 is nowhere near 15.
2*15 is nowhere near 1
2*5 is nowhere near 3
2*3 is one away from 5.

Whoops! We didn't find a difference of 2 It can't be factored. Stop trying.

2^2 - 4*2*(-15) = 4 + 90 = 94 is NOT a perfect square. Sure enough. We just PROVED that it cannot be factored using only Rational Numbers.
 
Well thats what I figured after trying for a few hours, but I had asked for help in the geometry section and the person who responded told me to factor that. I assumed based on that that it was factorable. Why not just tell me it is unfactorable then?

The original problem was:
The length of a rectangle is 1cm longer than its width. If the diagonal of the rectangle is 4cm, what are the dimensions (length and width) of the rectangle?

w^2 + (w+1)^2 = 4^2
2w^2 + 2w -15 =0

Am I supposed to use the quadratic formula then since it is not factorable?
 
jdruopp said:
2w^2 + 2w -15 =0
Am I supposed to use the quadratic formula then since it is not factorable?
YES. Any reasons why you don't know that?
 
you know people come on this site for help, not to feel like they are stupid. not everyone "gets" math.
And for your information, I did the quadratic formula and got some ridiculous answer. So I was asking if I should use the quadratic as "ressurance"
But rather than ask you if I did it right, I'll risk getting the answer wrong. I don't need to feel like I am dumb just because I dont' understand some stupid math problem that I will never use in my life.
I'm not some silly high school student. I am 30 year old veteran who is trying to get a degree after being struck by a car while walking across the street after coming home from Iraq. You think you are so smart because you know some math? Let me tell you something, you know nothing!!!
 
It is a strange thing to get a response like that. You have assumed much that doesn't exist. I'll give you the short version.

1) The only way for you to feel stupid is for you to choose to do so.
2) If there were a single soul here making an effort to make someone feel stupid, EVERYONE else would be on his/her back until it quit.
3) We are all volunteers. None of us is here to pat ourselves on the back so that we can be reminded how great we are. We just want to help struggling folks like yourself.
4) You came to us for help. Rather than get upset at the help you receive, consider its value. If we are a bit surprised that you spend 2 hours trying to factor something that can't be factored, it is obvious to us that you are missing something in your education. This should not be a surprise, since that may well be why you are here.
5) There is a very fine balance between hand-holding and encouraging. There is a very fine line between confrontational questions and leading questions.
6) We ALL would do well to remember why we are here. As long as you remember that we are on your side, and that it is not in our nature to be insulting, we will all get along just fine.
7) Let's learn some mathematics.
 
We are not on here to make anyone feel bad about themselves. Everyone who tutors on here is doing it because they care about helping someone else, "understand".

This board ranges from students in 4th grade doing simple arithmetic, to people with Phds. Everyone is at their own level, and that's what makes it a diverse and supportive community, because no everyone "gets it", the first few times...else no one would be asking questions, right?

I know, from being on here a while, that none of osters, (including Denis), want to hurt feelings or make math any more difficult than it is to the people asking the questions.

We are all here to support one another. We will support you as a student and help with what you don't understand.

Now, what are the steps you took with using the quadratic formula?

Best of luck!
John.
 
I dont' think anyone of the tutors maliciously tries to make the "student" feel stupid, however it is how the tutor writes his response. Such as, using capital letters to make a statement. Instead of saying -YES any reason why you dont know that? why not just say, yes using the quadratic equation should help you. I never asked anyone to do the work for me, I jsut asked for some help, not to be insulted. The reason I spent so long trying to factor an equation that couldnt be factored was because one of the tutors told me all I had to do was factor it (look in geometry section).

Thanks to all for the help in previous questions. The help I have received thus far has been been very helpful and has brought my grade up.
 
Just a little rebuttal -

I respectfully disagree that how something is written exposes the writer's intent. I have long disagreed with the premise in literature classes. The reader may construe what the reader wishes to construe. The writer can influence the reader, but it really is up the the reader how the reader feels about it. There is very, very, very little writing in my experience that could be taken out of context and presented to 100 people and have 100 of them conclude the author's intent consistently. It really is up to the reader. Put in this context of helpful volunteers, there really is no reason to conclude insult. There just isn't. Don't do it. Take responsibility for your own feelings.

An important reasiong for asking "-YES any reason why you don't know that?" rather than the alternative you suggested, is the emphasis on the fundamental nature of the concept. If, indeed, you do NOT know that, you need to back up a bit and get it, because somehow you missed it or misplaced it. It is very important. It should be given emphasis, as should other fundamental concepts.

Why did you put "student" in quotation marks? Were you quoting or were you demeaning the description? I don't recommend the latter.

I put the last section in just to demonstrate. If you are puzzled by something, simply ask. No need to be insulted. You have a choice.

I had a nice read in the geometry section. You were told to factor the equation. So? You assumed it was possible. In my view, the individual you told you to do that figured you knew enough about factoring. You were both wrong in those assumptions. This emphasizes the importance of your background. If you are just going to do whatever you are told, you are on a very slippery slope. You need not to do the things that will lead you into an endless loop of frustration. It would have been much more beneficial if you had proceeded as I demonstrated initially, namely, try to factor or prove that it cannot be done, then take another approach.

"I just asked for some help, not to be insulted" -- You know what I'm going to say about this, right? Insult is up to the reader. Don't choose it and we'll all be happier.

I hope sincerely that we can learn some more mathematics.
 
Sorry, it's just that I've been told what to do for the past 12 years of my life (in the military) so when that tutor told me to factor the problem, that's what I intended to do. Guess I'm just better at being told to kill the enemy than factor a stupid math problem

Again, thanks to all who have tried to help a dumb grunt like myself.
 
Hey jd, my yelling "YES" was really to "say unto ye" NOT to be affraid
to use the quadratic, even if the equation CAN be factored.

Like, why spend 1 hour trying to factor, when you can get the same
"factoring" done with the quadratic in a minute or so?

Thassa my opinion of course...
 
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