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#1 Re: Help Me ! » Find A Function » 2021-06-13 08:25:29

Bob wrote:

hi nycmathguy

Just discovered this post. 
Surely the cost goes up for each step up in w. 

I've got a 13 line function definition covering (0,1], (1,2], (2,3] ...(12,13] where an open bracket means don't include the endpoint and a square bracket means do include it. And then over 13 a statement that the function is undefined.

But it would be good practice for you to try and  and express lines two up to thirteen in a single expression using a suitable step definition.  The choices are floor, in which the charge is truncated down to the first lower integer, and ceiling in which the charge is rounded up.

Decide which of these two is the correct one and also find a suitable algebraic expression for the charge applicable.  You need to include the fixed charge for the first oz, and then the m value to reflect how the charge increases for each subsequent oz added.

In another reply I gave you a link to mathword where these two functions are illustrated.  The MIF function plotter will handle floor and ceiling so you can test your function by making a graph.

Bob

I will play with this problem some more.

#2 Re: Help Me ! » Slope of the Secant Line » 2021-06-11 09:18:45

Bob wrote:

Yes.  This is just like the question I have just done with y = x^3.

B

I will also play with this question some more on my days off.

#3 Re: Help Me ! » Slope of the Tangent Line » 2021-06-11 09:17:40

Bob wrote:

hi

https://i.imgur.com/ABnoIoX.gif

The secant line is just the slope of AB. You can use (y2-y1)/(x2-x1)

The wording for part b is muddled.  From part c I think this is what is meant:

For the table start with x = 3 and x^3 = 27 and your result from part a.  Then let x approach 2 from above. So fill in the table with 2.5, 2.1, 2.01, 2.001 etc.  You should be able to see a limit emerging from this.

Sorry, forgot to read to the end before doing the graph so I haven't put on the tangent.  You can easily do this yourself I'm sure as part c gives the m value and you know the line goes through (2,8).

Bob

I will further look into all 4 parts.

#4 Re: Help Me ! » Investigate Each Limit » 2021-06-11 09:15:39

Bob wrote:

hi

For question 1, you can start with x = 1.9  There's no need to go near negative values as we want to approach x = 2 and so there's no need for the absolute function at all.

Just treat this as sqrt(x-x)

Q2.  More information needed concerning the step function.

If you look here http://www.mathwords.com/f/floor_function.htm

and compare with http://www.mathwords.com/c/ceiling_function.htm

you'll see that two graphs are possible and it makes a difference to the limit.

Bob

I am not too familiar with the step function. I will check out the links.

#5 Re: Help Me ! » Complete Table Using Limits » 2021-06-11 09:14:00

Bob wrote:

Yes that's right.

But (small point)

Values for x: 2.001, 2.01, 2.1

I'm being very picky but this should be 2.1,  2.01, 2.001

as you're supposed to be getting closer and closer from the right.

Bob

Ok. I had the values x is tending to from the right in reverse order.

#6 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-11 09:12:13

phrontister wrote:

https://i.imgur.com/5OhyVzG.jpg

Here is my original link to the picture:

http://imgur.com/gallery/4l3aenO

What can you do with that?

#7 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-11 09:10:43

phrontister wrote:

https://i.imgur.com/5OhyVzG.jpg

How did you do that?
Can I provide you the link(s) for you to copy and paste my graphs and geometric figures? I don't have a laptop or computer. I have a cell phone and two tablets. I mostly do my postings via cell phone.

#8 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-11 02:01:17

phrontister wrote:
Bob wrote:

I tried adding the 'i' in i.imgur to the link but got a server error.  I also tried...[lotsa things]

Hi Bob;

Yes, been there, done that...with the same degree of success.

The post #7 link just gets me to some kind of gallery page, with the main item being the image. The ID number is wrong too, as it's very different from the number I got from clicking the image.

It's not an 'image' url as such, one with an image-format extension (eg, jpg or png)...in the form accepted by the BBCode img tags.

With the BBCode image links that are posted here on MIF, just the image shows up...nothing else. No gallery, no peripherals, no ads.

Solution: I suggest selecting the already-uploaded-to-Imgur image with the cursor (or however you do it on a phone), and demanding the recalcitrant dumb smartphone to jolly well cough up the image address!! faint


Enough is enough. Let's move on.

#9 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-11 01:59:53

Bob wrote:

I tried adding the 'i' in i.imgur to the link but got a server error.  I also tried putting one of my links into the post and that worked.  So I changed the imgur identifying code and it failed.  I conclude that phone app users don't get the same saved image structure.  I might try getting the app and then see what happens when I try the same.  Might be a while before I get round to this.

Bob

Can we move on?

#10 Help Me ! » Find A Function » 2021-06-10 19:40:10

nycmathguy
Replies: 2

As of January 2013, the U.S. Postal Service
charged $0.92 postage for first-class retail flats (large envelopes)
weighing up to and including 1 ounce, plus a flat fee of $0.20 for
each additional or partial ounce up to and including 13 ounces.
First-class rates do not apply to flats weighing more than
13 ounces.

Find a function C that models the first-class postage charged,
in dollars, for a large envelope weighing w ounces. Assume
w > 0.

I have been struggling with questions requiring a function to be constructed from written information. I believe that this is one of the most important techniques to develop in mathematics. In fact, sometimes I feel like concentrating on this skill above the rest.

The question posted here is number 60 (an even number question). There are no answers in the back of the book for even number questions.  So, I decided to use the answer to question 59 as a guide to make the function given below. Otherwise, I could not even begin to write the information as shown that may or may not be right.

Let c(w) be a piecewise function.

I think this is a four-part piecewise function based on the answer for question 59.

Let c(w) equal the following:

0.92     0 < w ≤ 1
1.12     1 < w ≤ 2
1.32     2 < w ≤ 3
1.52     3 < w ≤ 13

Is this right?

#11 Help Me ! » Slope of the Secant Line » 2021-06-10 17:35:30

nycmathguy
Replies: 2

Given  f (x) = x^2 − 1, find the slope of the secant line containing the points
P = (−1, f (−1)) and Q = (−1 + h, f (−1 + h)).

Solution:

By carefully looking at this problem, I think the first step is to
evaluate f(-1) and f(-1 + h). Is the second step to find f ' (x)?

#12 Help Me ! » Slope of the Tangent Line » 2021-06-10 13:54:40

nycmathguy
Replies: 2

Slope of a Tangent Line For f (x) = x^3:

(a) Find the slope of the secant line containing the points (2, 8)
and (3, 27).

Is this question asking to find m given the two points?
m = delta(y)/delta(x), where m is slope.

(b) Find the slope of the secant line containing the points (2, 8)
and (x, f (x)), x = 2.

The point (x, f(x)) = (x, x^3). Yes? Must I evaluate f(x) at x = 2? If so, what comes next?

(c) Create a table to investigate the slope of the tangent line to the
graph of f at 2 using the result from (b).

This is similar to the other thread posted about investigating the limit of a function using a table of values. Yes?

(d) On the same set of axes, graph f , the tangent line to the graph
of f at the point (2, 8), and the secant line from (a).

Since I cannot upload pictures, can someone please do part (d)?
Please, use different color lines to show the difference between the graph of f, the secant line and tangent line?

#13 Help Me ! » Investigate Each Limit » 2021-06-10 13:00:26

nycmathguy
Replies: 2

Use either a graph or a table to investigate each limit.

1. limit of sqrt{| x | - x} as x tends to 2 from the left.

2. limit of cuberoot{[ x ] - x}》as x tends to 2 from the left.

Note:

For question 1 in the radicand, we have the absolute value of x minus x.

For question 2 in the radicand, we have the step function [ x ] minus x.

I prefer the table method. What values of x can I use for each function as x tends to 2 from the left side?

#14 Help Me ! » Complete Table Using Limits » 2021-06-10 12:45:09

nycmathguy
Replies: 2

Complete the table for f(x) = x + 3 as x→2 from the right and left.

x tends to 2 from the left

Values for x: 1.9, 1.99, 1.999

x tends to 2 from the right

Values for x: 2.001, 2.01, 2.1

Solution:

I think this question is just an evaluation exercise.
I plug all the given x values to evaluate f(x) as x tends to 2.

Each value of x from the left and right gets me closer to 2 but never reaches 2, which is the basic limit idea.

Yes?

#15 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-10 12:33:42

Bob wrote:

If you do what you did the other day using imgur then I can see your diagrams quite satisfactorily.  They just don't appear embedded in the post.

I'm not sharing my email address with you so please stop asking.  I've already told you I don't do Facebook.

Let's start on some maths.

Bob

I will copy and paste the link that shows the image. You can then copy and paste the link in your url to see the picture.

Moving on....

Back to limits.

#16 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-10 12:31:14

phrontister wrote:

I don't have a smartphone and don't know much about them, but anyway, here's something that may help re this image problem...

I was able to view the image on my PC via the link from post #7. However, I suspect that the link isn't to the image itself, because Imgur image urls begin with 'https://i.imgur.com/' (different from nyc's 'http://imgur.com/gallery/'), and include a file extension (eg, '.jpg') after the filename (which nyc's doesn't).

That could account for the image not displaying here.

When I right-click the image in Imgur and select 'Copy image address', like so...

 
...I'm given the url 'https://i.imgur.com/ZVsL4f8.jpg', which agrees with the starting format I mentioned above.

Entering that url between img tags successfully displays the image:

However, that image size is way too large for forum viewing (well, on my PC it is), so I shrank it to 640x480 for comparison:

The shrunk size fills just over half the width of my screen, which is about right for me.

What do you mean by "Entering that url between img tags successfully displays the image:"?

#17 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-10 10:54:27

phrontister wrote:

I don't have a smartphone and don't know much about them, but anyway, here's something that may help re this image problem...

I was able to view the image on my PC via the link from post #7. However, I suspect that the link isn't to the image itself, because Imgur image urls begin with 'https://i.imgur.com/' (different from nyc's 'http://imgur.com/gallery/'), and include a file extension (eg, '.jpg') after the filename (which nyc's doesn't).

That could account for the image not displaying here.

When I right-click the image in Imgur and select 'Copy image address', like so...

 
...I'm given the url 'https://i.imgur.com/ZVsL4f8.jpg', which agrees with the starting format I mentioned above.

Entering that url between img tags successfully displays the image:

However, that image size is way too large for forum viewing (well, on my PC it is), so I shrank it to 640x480 for comparison:

The shrunk size fills just over half the width of my screen, which is about right for me.

Can you provide the steps? What exactly must I do here?

#18 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-09 09:48:22

Bob wrote:

Android is perfect.  Photobucket offers a similar service to imgur and does enable BBCode for android operating systems.  So the Photobucket app should allow you do insert images into your posts.  I'll try it myself later today.

later edit:  I've spent an hour chasing around the photobucket site trying to get the BBCode.  Why don't companies have a manual these days? Eventually found the link but it's greyed out.  More chasing around to find out why.  Finally got to a screen that says I've got to pay up to get this feature.  Really?  I really object to having my time wasted like this.  They said it was a feature, and it may be, but they 'forgot' to say that the free app doesn't do it.  Once again I'm so sorry.

Back to the drawing board.  Anyone else on MIF found a way to do this on a mobile?

Bob

I understand what you're saying.

My question again is:

Why not simply communicate via email?

I can create a calculus file for me to keep my questions and your replies for extra study and practice. I can take a picture of the graph or geometric figure and attach it to the email for you to see. Why is this not a good idea?

#19 Re: Help Me ! » Can't wrap my dumb head around this angles problem » 2021-06-08 12:28:19

Bob wrote:

Hi, Your three equations are correct, so this ceases to be an angles question and becomes an algebraic one.
Add together the first two (2p + g + h) and subtract the third to get p.

Bob

Is this not three equations in 3 unknowns?

#20 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-08 12:26:39

Bob wrote:

Question: i phone or Android?

Bob

Android.

Samsung A-21.

#21 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-08 12:25:16

Bob wrote:

hi nycmathguy

I've spent some time trying to sort this out.  I can insert a link to one of my images into your post and that works.  I've tried modifying your link so that it is identical to mine (replacing my link with gallery/4l3aenO) but that gets a forum software error.

So I've downloaded the imgur app and signed in.  I couldn't find a way to get the BCCode so I searched through the FAQs for the app and sad found that the phone app doesn't have this feature.  So, at the moment, imgur isn't the solution.  Sorry to have misled you but I have only ever tried the phone app today.

There must be an alternative app that will work.  I'll go searching and let you know if I can find anything.

If I copy and paste your link into the address bar of my browser I can get your image so I have been able to view it but not embedded into a post.

A workaround would be to log in to imgur at an internet cafe.  Have to be a good image though, as it'll cost you the price of a coffee smile

Bob

Hey brother, don't worry about it. In terms of the cafe, this does not work for me. No internet cafe nearby. I wouldn't go there anyway. Not my style, not my thing to do.
My solution is the easiest.

1. Let me have your email address. I can attach pictures of functions and geometric shapes.

2. Search for me on FB. I can create a Calculus Private Group where my questions with pictures would be posted.

3. My phone is android. A-21 Samsung.

#22 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-07 09:40:03

nycmathguy wrote:
Bob wrote:

hi nycmathguy,

When I use Imgur I use a browser connection on my laptop.  I don't know how different the app is but somewhere there should be a set of options like this:

https://i.imgur.com/Y8hTnmK.gif

This is the forum friendly BCCode link so the forum's software knows where to find the image to imbed in your post.

So you copy the BCCode line (I've ticked the one you want) into your post and when you submit it the picture should appear in your post.

Let me know how you get on.  If your next post has an image, I'll know you've 'cracked it'.

Bob

I will go back to the app now and try again. We are almost there.

There is no set of options in the app. Should I edit my original thread and click BCCode?

#23 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-07 05:59:33

Bob wrote:

Nearly there.  Look again at the list of imgur options.  The one you need to choose is called BCCode message boards and forums and has the link inside img tags.  Try that and hopefully it will work.

Bob

I will try one more time later this evening.

#24 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-06 05:30:17

Bob wrote:

hi nycmathguy,

When I use Imgur I use a browser connection on my laptop.  I don't know how different the app is but somewhere there should be a set of options like this:

Y8hTnmK.gif

This is the forum friendly BCCode link so the forum's software knows where to find the image to imbed in your post.

So you copy the BCCode line (I've ticked the one you want) into your post and when you submit it the picture should appear in your post.

Let me know how you get on.  If your next post has an image, I'll know you've 'cracked it'.

Bob

Here is the link of the attachment:

http://imgur.com/gallery/4l3aenO

No image has been displayed.

I'm just not getting this stuff. I am not too savvy in terms of technical stuff.
I have a better idea. If you are truly interested in helping me with calculus, here are two best options:

1. Let me have your email address. I can text my book questions to you and picture attachment when needed.

OR

2. If you are on FB, I can easily create a Calculus Group. We could interact the way as well.

I'll wait for your reply.

#25 Re: Help Me ! » Investigate Limit For Piecewise Function » 2021-06-06 05:01:38

Bob wrote:

hi nycmathguy,

When I use Imgur I use a browser connection on my laptop.  I don't know how different the app is but somewhere there should be a set of options like this:

https://i.imgur.com/Y8hTnmK.gif

This is the forum friendly BCCode link so the forum's software knows where to find the image to imbed in your post.

So you copy the BCCode line (I've ticked the one you want) into your post and when you submit it the picture should appear in your post.

Let me know how you get on.  If your next post has an image, I'll know you've 'cracked it'.

Bob

I will go back to the app now and try again. We are almost there.

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