EMERGENCY-Need help using graphing calculator app-exam thursday evening 2/17/11!!

[applemagic123]

Now I know this question has not been asked...I'm in a college algebra class. Not a remedial course. I have NEVER used a graphing calculator in my ENTIRE life, and I now need to use one. I need to learn how to use a graphing calculator "iPhone style" as it is not at all like a real graphing calculator...you have to do the functions and different inputs differently and stuff. The professor went over how to do a problem using a real grapher, but I couldn't figure it out on my iPhone app. The specific app I have is by William Jockusch, for 99 cents, "Scientific Graphing Calculator."

**I'm willing to spend money on a couple of other graphers if you guys recommend better ones. I am on iOS version 3.1.3 on a 2g iPhone, so I cannot install 4.xx only apps.

The problem is as follows: For the function f(x) = -5x^2+25x-48 Find the maximum or minimum value. The answer is: maximum value is -67/4 (I'm just not sure how to get to the answer.)

Before I say what I'm going to say next, let me inform you guys that what I got (the graph) on my iphone app did not look at all like how it did on the graphing calc that my professor was using. (he did it on a large projector on a white wall) my iphone app showed an upside down (reflected about the x axis) super stretched and skinny standard parabola.

My professor explained as follows:
Step one: go to "y=" and input -5x^2+25x-48
step 2: click "graph"
step 3: click "zoom fit" to actually see the graph
Step 4: hit "0" (this was where I got LOST and stopped listening and just played around with the app figuring how to do what he was explaining but just couldn't figure it out for the life of me. I was thinking to myself at this point, "oh god, I'm going to have to google this and it ain't gonna be pretty!" He ended up somehow getting a number for the max and min values and then converting it to a fractional (a/b) form.

Please someone teach me, and/or recommend other grapher apps if possible. Whomever can do this will be my god (figuratively speaking, not literally, haha)

 

[Surely]

Go buy a proper graphing calculator and learn how to use it.

There is no way that you can bring your iPhone into a college exam.

I'm guessing it's an emergency because you've left it to the last minute.....

 

[motulist]

Your prof won't let you use your iphone on the test. Just buy the calculator that your prof recommended (I'd guess it's the ti-83), it'll be worth it for the lack of hassle alone.

 

[applemagic123]

Your prof won't let you use your iphone on the test. Just buy the calculator that your prof recommended (I'd guess it's the ti-83), it'll be worth it for the lack of hassle alone.

Ok, who sells them cheapest (considering I can't go the amazon.com or ebay route this time)? costco? staples? office depot? etc?

Is a real one pretty easy to use? Is it self explanatory at all (kinda like a mac...I guess?) I'm just scared if I will need more than a day to learn learn. I still technically have 2 days, since it's a night class, but still.

As per the first responder, I had no idea I would need a grapher THIS early in the semester. I only thought I would need it for matrices.

 

[motulist]

Ok, who sells them cheapest (considering I can't go the amazon.com or ebay route this time)? costco? staples? office depot? etc?

It really depends on where you live, so there's no way any of us will be able to answer that question for you. Call around, the stores will probably tell you their price over the phone. Good luck.

 

[vistadude]

In most graphing calculators, one you plot a quadratic function, you can search for the minimum/maximum on the graph, or look for zeros if it crosses the x-axis. He actually did it wrong because there are no zeros for this plot.

The best way you can do this is to do it by hand, as you should be required to know this for basic maths later in life.

Take the derivative and set it to zero: f'(x) = -10x + 25x = 0.
Solve for x: x = 5/2
Then plug x back into f(x) and you'll get f(x) = -67/4

 

[vistadude]

Also take the second derivative which you'll find is -10. A negative second derivative means that you're solving for a maximum. If it were a positive second derivative, it would be a minimum.

 

[motulist]

Is a real one pretty easy to use? Is it self explanatory at all (kinda like a mac...I guess?)

It'll certainly be MUCH easier than trying to convert your prof's instructions into the the steps you need to perform in an entirely different calculator app. So just get the recommended calculator asap and do the best you can. If you need help on that calculator once you have it in your hands, then go to a ti-83 forum on a different website and see if you can get help there.

 

[vistadude]

I totally agree on the Ti-83. It's the easiest to use graphic calculator and will take you through lots of courses. The included manual is also very good for these sorts of things.

It'll certainly be MUCH easier than trying to convert your prof's instructions into the the steps you need to perform in an entirely different calculator app. So just get the recommended calculator asap and do the best you can. If you need help on that calculator once you have it in your hands, then go to a ti-83 forum on a different website and see if you can get help there.

 

[siurpeeman]

Also take the second derivative which you'll find is -10. A negative second derivative means that you're solving for a maximum. If it were a positive second derivative, it would be a minimum.

it's a college algebra class, not first year calculus. talk about second derivatives and concavity all you want, but it won't help him.

 

[Surely]

As per the first responder, I had no idea I would need a grapher THIS early in the semester. I only thought I would need it for matrices.

No idea? Don't you have a syllabus for the class?

This early? Isn't it close to halfway through the semester if it began in January?

Good luck OP......seems like you really, really need it.

 

[applemagic123]

No idea? Don't you have a syllabus for the class?

This early? Isn't it close to halfway through the semester if it began in January?

Good luck OP......seems like you really, really need it.

The class started on the 18th of january. We are barely into the first 1/4 of the semester. Anyway, the professor is an idiot, has no direction in his lectures, doesn't clarify things, when people ask questions, his answer doesn't really help. His syllabus doesn't coincide with what's going on in class. I've had good professors, and bad ones, this one is a bad one. I've had to teach myself EVERYTHING thus far. I think I'm going to make a complaint about him when I find out how to do that after the exam when I have more time. A handful of info he has lectured on was important which I actually grasped something from, but most of it I had to learn by reading the textbook. He knows what he's doing on the marker board but he doesn't know how to teach it.

Siurpeeman stated, "it's a college algebra class, not first year calculus. talk about second derivatives and concavity all you want, but it won't help him. "

Yah, I don't even know what a 'derivative' is. I know the problem in the first post is pretty easy, but the professor nor the textbook tought how to do the problem. The only way the professor explained how to do it was on a grapher. I guess if I study everything else real hard, I can manage getting that question wrong. There's 25 questions on the exam, I'm assuming it's going to be easy if I study hard, considering someone on ratemyprofessors.com stated that his tests are easy if you study well.

Anyway, can someone explain it again without using weird math terminology like "derivative" please?

 

[siurpeeman]

Anyway, can someone explain it again without using weird math terminology like "derivative" please?

it's difficult to explain without knowing what you know/don't know. but basically, the max/min value of a quadratic function (parabola) occurs at the vertex. assuming the parabola opens vertically, the x-coordinate of the vertex tells you when the max/min happens, and you find this by finding the axis of symmetry. the y-coordinate of the vertex represents the actual max/min value. you find this by taking the value of the axis of symmetry and substituting it in for x in the original equation.

things you need to look up, preferably in your textbook:

• axis of symmetry (not the most helpful link but it gets the job done)
  
• how to find vertex

 

[Sparky9292]

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I've bought all of the graphing calc apps on the app store. As of now there is simply no app that comes close to all of the features on an old $20 used TI-83 Plus. In addition, many developers don't try since iPods and iPhones are banned from tests.

By the way, the max or min value on your polynomial can be found by plugging in x=-b/2a. I assume you are not taking calculus.

 

[applemagic123]

Umm yah! All the app store apps suck! I bought myself a ti-89 titanium. It has "apps" and even has a notes app, which I put alllll the formulas into! Haha!!

 

[Vice92]

The Ti-89 is one of the best calculators ever made, but the wolfram alpha app will do everything the calculator can, and will show you the steps.