Math Is Fun Forum

Hi Phro,

I'm using Android.  Tried all sorts of image sharing but have yet to get the bcc version. Elsewhere on the help it says bcc is not an option for mobiles

Bob

hi imcute

As you are new you perhaps won't have been following the difficulty here over a number of threads.  On a previous server it was posssible to upload images directly to MIF but difficulties with that server meant the forum had to swiitch over and the direct upload facility was lost.

I use Imgur to get images here using a bcc code address from Imgur.  I advised harpazo1965 to do the same.  He signed up and uploaded his image there but the site does not support bcc on their mobile app, so this hasn't helped him.

If you know a way to get an Imgur image into bcc format on a mobile we'd all be really pleased to know it.  Or maybe you know another way for him to get images here.  Thanks.

Bob

Tried this and I get an Imgur 404 error.

Bob

That should work but I still think the graph is the key. Once you have that the algebra is easy.

Bob

Many thanks, Phro.  That's just what I needed. I'm gong to take out your hide tags to see if the image shows as was wanted.  If so, you have found a way to get the image onto MIF from imgur. Yay! It works!

As to the poster's question its simply this.  All x lies between minus infinity and plus infinity so why waste space including an inequality.

Bob

It's got a vertical asymptote at x=3. And a horizontal one at y=1.

If you attempt to solve for y=1 you get no x value.

So that's a clue. Try to construct the graph

Bob

There is a on-line maths course that objected because we were 'publishing' their worksheets. They threatened 'breach of copyright' action.

So you need to take care what you post.  If you have a question that you think is good practice for a particular exam, post it in Exercises. Post one question at a time rather than collecting up a whole set and posting all in one go.

Bob

hi harpazo1965

For my question you have correctly identified two values that are outside the domain.

The vertical lines x =-1 and x = + 1 are asymptotes.  If you're not sure what that means have a look at Jade's post about a domain and range question here:

http://www.mathisfunforum.com/viewtopic.php?id=27953

My initial answer was limited because I was only working from a phone.  Later I was able to add a graph that, I think, makes it clearer.  I would certainly say that the graph is the key to domain and range questions.

Looking at your final answer you don't say what happens between the asymptotes ... ie between -1 and + 1.  Do you think there are no x values there?  Easy to show that's wrong because x = 0 gives y = -5.

I'll leave you to ponder that.

Bob

hi

In questions about domain the assumption is that it will be all real numbers unless there are values of x that do not lead to values of y.

infinity is not a value that y can ever attain.

This is why you set the denominator to zero to see if x vales might lead to the graph 'zooming' up towartds infinity. You didn't find any so no reason not to have the whole set of real numbers as the domain.

The 'rule' is all reals unless there is a good reason to exclude some x values.

There are other reasons.  For example the square root function has to be limited to x ≥ 0 as you cannot find a real number that is the square root of a negative.

If you wanted to devise a function to calculate the cost of theatre tickets  where the input is 'n' the number of people wanting tickets you'd have to exclude everything except whole numbers . You might allow zero and you might have a top limit to n based on the size of the venue.

Try y = 5/x^2-1) for comparison.

Bob

I've spent 30 minutes trying to make this work; finally resorting to the Imgur help site.  They say bcc codes are only available on desktop devices.     So sorry

From the internet chat surrounding this difficulty there are lots of unhappy image posters out there.

You can get the https adress of your image like this:

Log in to Imgur.

Click the person icon (bottom right on my screen) and your images appear.

Select the one you want and click the right arrow.

Click copy url.

Log in to the forum and start a post.

On the text input screen press and hold to get the paste option.

This will give you something like this:

https://imgur.com/a/BURsC8w

This track car picture was needed when I was helping a guy with his car frame geometry.

Anyone can copy and paste this into a fresh browser tab to view your image.

NOTE TO OTHER MEMBERS: Can anyone recommend a good image hosting site that does support bcc codes when using a mobile.

Bob

5.04 x 10^(-1)

B

hi harpazo1965

See https://www.bbc.co.uk/bitesize/guides/z … revision/1

Your arithmetic is correct but it is best to leave the powers of ten if you want to end up with standard (index) form.

So a number between 1 and 10 followed by a power of ten.

Back in the days before calculators logarithm tables were often used to do calculations.  A table book usually had the logs of numbers between 1 and 10 so having numbers in stardard form made this easier.

eg.  In base ten log 2 ≈ 0.3010 ; log 20 = 1.3010 ; log 200 ≈ 2.3010 ; log 0.2 ≈ -1 + 0.3010 ; log 0.02 ≈ -2 + 0.3010 etc.

Page 6 of that BBC bitesize shows a calculation using standard form and page 7 shows how a calculator displays numbers that are too big |(or small) to fit the screen size.

Bob