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Old 04-19-2012, 12:22 PM   #8341
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Quote:
Originally Posted by gunsnroses#1
So I cannot factor to save my life , can someone please explain step by step how to factor this
x^2 +4x-77

What two numbers add to give +4 and multiply to give you -77?
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Old 04-19-2012, 12:28 PM   #8342
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Originally Posted by KeepOnRotting
What two numbers add to give +4 and multiply to give you -77?


11 and -7?
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Old 04-19-2012, 12:32 PM   #8343
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Quote:
Originally Posted by gunsnroses#1
11 and -7?

Indeed. Those are going to be the second terms inside your brackets. Now what gives you x^2? Once you figure those 3 things out, factoring this way is no problem.

It comes down to (using Ax^2 + Bx + C = 0):

1) Figure out what 2 terms multiple to give you your first term (Ax^2)
2) What two numbers add together to give you the B portion of Bx
3) What two numbers multiply to give you C


Once you have your terms in brackets, multiple the brackets together using FOIL to make sure your answer is right.

Last edited by KeepOnRotting : 04-19-2012 at 12:33 PM.
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Old 04-19-2012, 12:45 PM   #8344
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Quote:
Originally Posted by gunsnroses#1
So I cannot factor to save my life , can someone please explain step by step how to factor this
x^2 +4x-77

1. Think of all the factors of the last term (77). You can get (1,77) and (11,7)
2. Look at your second term (4). See if any of your factor pairs have a difference between them equal to the second term. 11 and 7 fit this bill.
3. The sign of the second term is positive, so the larger factor has to be positive in order for that middle term to be positive as well. This causes us to say one of the factors is (x+11).
4. Think of FOIL. In order to get the last term to be negative, the other term must have a minus sign. The other factor is therefore (x-7).
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Old 04-22-2012, 10:06 AM   #8345
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Quote:
Originally Posted by gunsnroses#1
So I cannot factor to save my life , can someone please explain step by step how to factor this
x^2 +4x-77

A good way to remember how to factor this things is to write it as already factored:
(x-a)(x-b) = x^2-ax-bx+ab = x^2 -(a+b)x + ab = x^2+4x-77

Then you have:
-(a+b) = 4
ab = -77
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Old 04-22-2012, 03:50 PM   #8346
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can someone show me how to simplify sinx(-cosx/sinx)? I know the answer is -sinx but that doesn't make any sense to me. I would think it would be -cosx since im pretty sure the sinx's cancel.
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Old 04-22-2012, 04:23 PM   #8347
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Quote:
Originally Posted by funkbass369
can someone show me how to simplify sinx(-cosx/sinx)? I know the answer is -sinx but that doesn't make any sense to me. I would think it would be -cosx since im pretty sure the sinx's cancel.
Umm...it should be -cosx ... why would it be -sinx?
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Old 04-22-2012, 04:32 PM   #8348
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Quote:
Originally Posted by FishStik
Umm...it should be -cosx ... why would it be -sinx?


that's what the answer says on my homework.
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Old 04-22-2012, 04:38 PM   #8349
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TEACHER ERROR! Never let him hear the end of it.
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Old 04-22-2012, 04:41 PM   #8350
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Originally Posted by FishStik
TEACHER ERROR! Never let him hear the end of it.


He doesn't make the homework. It's done by some textbook company. There seems to be a lot of errors in the answers on our homework though. It's confusing because I never know if I'm doing something wrong or if there is just an error. And then I lose points because the answer key is wrong.

anyways, that's how that problem is done right? just cancel out the sinx's?
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Old 04-22-2012, 04:42 PM   #8351
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Only if x=Pi/4....
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Old 04-22-2012, 04:45 PM   #8352
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Only if x=Pi/4....


the x's are irrelevant in the problem. I just used x's because I didn't feel like figuring out how to type a theta symbol on my keyboard.
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Old 04-22-2012, 04:46 PM   #8353
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Quote:
Originally Posted by funkbass369
anyways, that's how that problem is done right? just cancel out the sinx's?
Yep. If you don't trust the answer key, Wolfram is your friend. Just don't abuse it.
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Old 04-22-2012, 04:48 PM   #8354
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Originally Posted by funkbass369
the x's are irrelevant in the problem. I just used x's because I didn't feel like figuring out how to type a theta symbol on my keyboard.


Sure. I was half-joking, because sin(Pi/4)=cos(Pi/4). No worries, your answer is the correct one. The sin's cancel. The only place where you have to watch out with canceling functions like that is when the denominator becomes zero. It is often advisable to treat those cases separately. However, in this case I think it's fairly obvious that the limit as x->0 sin(x)/sin(x)=1.
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Old 04-22-2012, 05:36 PM   #8355
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Originally Posted by FishStik
Yep. If you don't trust the answer key, Wolfram is your friend. Just don't abuse it.


thanks a lot for the site. it sucks when you get a C on a test just because the answer key to the homeworks and test reviews are usually wrong.
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Old 04-22-2012, 05:51 PM   #8356
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No probs. You'll find yourself using it more frequently as you get to higher math classes. That 'show steps' button is nothing short of magical.
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Old 04-25-2012, 03:50 PM   #8357
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Doing some science project on concrete and I need help.

Before you ask; no, I don't want you guys to do my homework for me, I'd just like to understand what I'm doing Anyways, here are some questions I need help with...

1. What type of treatment is used in industry while preparing alloys like steel? (Surprsingly had a hard time finding this on google...)

2. How can pH influence the speed of corrosion?

3. (There's a diagram of oxidation reactions)
b) What are the products formed called?
c) Do them etals gain or lose electrons?
d)What atmospheric substance may promote the mobility of electrons?


Again, thanks if any of you guys can help me out with these and hopefully help me actually understand this (I've researched but had a hard time understanding some things ahaha...)
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Old 04-25-2012, 04:18 PM   #8358
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2. Rusting is a redox reaction. Most Redox reactions require H+ or OH-. By Le Chatelier's principle, increasing the reactants will drive the reaction forward. Hope that points you in the right direction.

3. I would prefer to see the diagram before answering this. Are you sure that it is an oxidation process? If it is indeed an oxidation process, the metals will lose electrons. I'm not sure what the products will be called because I'd have to see the reaction in order to predict the products; unless you teacher is looking for a generic term such as Reducing Agent or an Oxidizing Agent.
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Old 04-25-2012, 04:25 PM   #8359
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Quote:
Originally Posted by metal4eva_22
2. Rusting is a redox reaction. Most Redox reactions require H+ or OH-. By Le Chatelier's principle, increasing the reactants will drive the reaction forward. Hope that points you in the right direction.

3. I would prefer to see the diagram before answering this. Are you sure that it is an oxidation process? If it is indeed an oxidation process, the metals will lose electrons. I'm not sure what the products will be called because I'd have to see the reaction in order to predict the products; unless you teacher is looking for a generic term such as Reducing Agent or an Oxidizing Agent.


The diagrams for 3 are:

2Cu + (oxygen) = 2CuO
4Al + 3(oxygen) = 2Al(2)O(3)
4Fe + 3(oxygen) = 2Fe(2)O(3)



EDIT: Yeah, I'm pretty sure he's looking for a generic term...I mean, it's an easy question, I just probably don't know the term/he expects us to know this/We never learned it/I'm just stupid.

Yeah well, for number 2...I'd think that more oxygen = faster rusting? and since OH- (what makes something basic) contains oxygen...a higher pH makes the rusting process faster? But then if that's true, why would they put steel slabs in concrete...(concrete has a pH of 11)...woiuldn't that mean the steel would rust faster?
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Old 04-25-2012, 04:44 PM   #8360
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Does anyone have any tips for solving trigonometric identity problems?

I can't click with them at all and although they don't make up a large part of my exam I don't want to lose marks unnecessarily and have weak points.
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