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[WWfeedback] Section_10.2 prob:19

***** The feedback message: *****

How do I find the diagonals of problem 19 in Homework 10.2?

In answer to your question, parallelograms are all about vector addition.  You should plot the vectors, plot the parallelogram they form the sides of, and identify the diagonals in terms of operations on the two vectors

[WWfeedback] course:Taylor_MAT_267_Fall_2015:Section_10.2 prob:11

Hi Dr Taylor,
I've worked through this one a few times and get the same
answer. I've tried giving WebWork answers with greater precision with no
joy.

Let T be the tension in the clothesline.
Then 2T cos Ɵ = m.g

The angle is arctan(1/7) = 8.1301°
Then 2T = (4 * 9.8) / cos(8.1301°)
2T =39.598 N
Then T = 19.799 N

Am I missing something?

First of all, for everybody's benefit here is a link to my discussion of this problem a year ago.  Your equation 2T cos Ɵ = m.g follows from the idea that the sum of the two tensions should balance the force of gravity, hence be vertical, and that the sum is twice the vertical component of either tension.  The magnitude of both vertical components is T cos Ɵ where  Ɵ is the angle formed between the rope and the vertical direction.  Eye-balling it suggests that this should be quite a bit larger than the 8.1301°, so I think you have the wrong angle...and in fact the opposite of this angle is 7m and the adjacent is 1m, so you should have had the formula Ɵ=arctan(7)=1.429rad=81.89°.
Then 2T = (4 * 9.8) / cos(81.89°)=277.19 etc.

[WWfeedback]: Section_10.2 prob:10

Hi Dr. Taylor,
I'm having some trouble with the second part of this
question. I initially used the equation 5=sqrt(194)cos(a) to find a (the
angle). And when I did that, I got the answer of 1.2 rad, which came back
wrong. So, I tried subtracting 1.2 rad from pi/2 to get 0.37 rad, which
also came back wrong. It turns out you get the same answers using
tan^-1(a)=13/5, and u*v=|u||v|cosa, where u= (5, 13) and v=(0, 13). How
should I try to approach this problem?
Thank you,
**************

the only mistake you are making is that WebWork is expecting three decimal places of accuracy

[WWfeedback] course:Taylor_MAT_267_Fall_2015 Section_10.2 prob:1

On Thu, Aug 27, 2015 at 3:12 PM, ************ wrote:

 ***** The feedback message: *****

 I dont understand what i put in for |a|

This is a situation I mentioned in class: some people (like us) use ||a|| to denote the length of a vector a, but some other people (the webwork folks, obviously) use |a| to denote the length of a.  You need to compute the length of a to do this part of the problem.

Lecture Notes Week of 8/23/15

...at the following links:
Lecture Notes 8/24/15

Lecture Notes 8/26/15

Lecture Notes 8/28/15

Homework Due September 4

Section 10.2 and Section 10.3.

Webwork problems

On Thu, Aug 27, 2015 at 2:03 PM, ********* wrote: When I attempt to access the homework it states that I am not authorized to do so and no homework assignment is displayed for me. Perhaps this is due to the fact I ended up signing up for the class late due to transcript troubles and I am not cleared for some reason. Anyhow, I hope that I will be able to access the system in time to turn in my assignments. 

 Apologies for being so late, I had assumed there would be no troubles and that I could do them today. 

Since you have an correct account on Webwork (I just checked), there are two likely reasons you're unable to access the webwork.
 1) your login is expired. Fix: re-login to ASU, then go to webwork as usual.

2) you are logged into another, non-ASU google account. Fix: log off of your google account, then re-login to ASU and go to webwork as usual.

(PS, you can nearly always expect awkwardly implemented software dev when dealing with almost any bureaucracy.  Assuming that there would be no troubles has cost me personally a lot of money, and it's a bad mistake for you to do so.)

[WWfeedback] course:Taylor_MAT_267_Fall_2015 user:******** set:Section_10.1 prob:14

***** The feedback message: *****

Hi Dr Taylor,
I am a bit stuck on this one. I'm pretty sure I have parts 1,3 & 4 correct, but part 2 has me stumped.
According to my calculations,part 2 should have a centre at (2,2,1) with a radius of 0.5.
(x-2)^2 +(y-2)^2 + (z-1)^2 = 1/4
From what I can see none of the available spheres match that description. I have gone over my work several times but can't see where to go from here.

Any pointers would be greatly appreciated.

You completed the square correctly; the left hand side of the equation is indeed
(x-2)^2 +(y-2)^2 + (z-1)^2; this means that you added 4+4+1=9 to the left side so you must add 9 to the right side of the equation as well. This gives -35/4+9=-35/4+36/4=1/4--which is what you got, so you were correct that the radius-squared of the sphere is 1/4, hence the radius is 1/2. This means that you are looking for a sphere with radius 1/2, hence diameter 1, centered at (2,2,1). At this point, I have to agree with you that none of the sphere images looks very much like the sphere with radius 1/2 centered at (2,2,1), however, both D and F seem like they should have radius 1/2. F seems like it's center is (2,0,0), while D seems like it has a center (x,y,z) where y looks close to 2, z looks close to 1 and x is positive, so I choose D, which turns out to be the correct answer.

New Office Hours

If I've done my math correctly, the following schedule will accommodate everyone who took the office hours poll in at least one office hour per week

Mon 11:30-12:30
Tue 11:00-12:00
Thu 11:00-12:00

the last word on "the" textbook

On Mon, Aug 24, 2015 at 12:29 PM, **** *** <****.***@asu.edu> wrote:

I suppose they will all do Tom. Sorry for the delay

---

From: Thomas Taylor [tom.taylor@asu.edu]
Sent: Friday, August 21, 2015 12:38 PM
To: ******
Subject: mat267 textbook

Hi ****, can you advise?  There are apparently different versions with different ISBN numbers of Stewart's Essential Calculus , Early Transcendentals 2nd Ed floating about.  Is there a real one, or will they all do?

thanks,

Tom Taylor

Office Hours for This Week

Office Hours for this week are MWF 11:30-12:30.

a little bit more on anonymous access to webwork

Hi ******** *******
ah, that's too bad. 
Thanks very much for your quick reply.

--Tom

On Sun, Aug 23, 2015 at 10:22 PM, ******** ******* <*******@asu.edu> wrote:

Tom:

for security reasons ASU required us to change the authentication system. This new authentication system  bypasses the webwork login page and goes directly to the ASU login page. This means there are no more Guest logins.

I am meeting this week with one of Renate's students to see whether we can change this, but I doubt we will be able to .

Khan Academy playback speed settings.

Dear Professor Taylor,

In class yesterday we were talking about the wonderfully helpful site Khan academy. I mentioned that his videos get long and dull and put me to sleep easily but I found that you can speed up his videos so its not as bad. You wanted me to send you an email telling you how to do it so here goes.

When watching Khan's videos there is a gear sprocket in the lower right hand corner.

Click on that and then a menu pops up where you can change the quality of the video and hide or show annotations but there is also an option for speed.

Click on speed and you can change the speed of the video to make it faster or slower.

Hope this is helpful,

*************

Thanks, this is useful info!  For those who haven't been there before, this link will take you to a lecture that's good background for our lecture tomorrow, and at the little sprocket you can set the speed--I find the 1.25x setting to be about right for me

guest/anonymous access to webwork

Hello:
     I recall you recommending us to try to preform homework
problems signed in as "Guest." How do I sign in as a guest on WeBWork?
Thanks:
     *******
<and>

Professor Taylor,

Hello, my name is **** ******** and I am in your
MAT 267 class, section 72768. How can I access the homework as a guest to
work on problems before completing the homework for a grade? I have not
used this feature of WeBWork before. Thanks.

Sincerely,
**** ********
<and>

Good Afternoon Professor,


I was looking over WebWork, this being the
first time I have used it, and would like to know how exactly do you work
the homeworks as "Guest". Also on the syllabus, you mentioned there being
an "introduction set". Again, I would like to know where I can locate this
to get better accustomed to WebWork.


Thank you for your help,
**** **** *******

My apologies, for two reasons.  First, I meant to say access webwork as anonymous/student to do the practice problems first.  Second, I find that I'm not able to access the practice problems online myself--I am corresponding with the webwork systems admin on this issue.   I do find that if I login to my own account, at the bottom I can click on the button "Download PDF or TeX Hardcopy for Current Set" which will let me choose to download one of the practice sets.    I'm not sure you can access these hardcopies in the same way, so here is a link to one version of the hardcopy.  I realize that this is not as useful as having webwork tell you when you've done a problem but at least you can get started.

On the importance of the textbook....

Hey Thomas, this is ******* and I have your class this Friday. I was just wondering about something because I don't have my book yet but i should have it by next week will that cause any problems with tomorrow class?

Well...no, yes, and maybe.  No, I'm not going to police if you have the textbook or not, it's your textbook and you can do how, where and what you want with it.   Yes, your first homework assignment opens tomorrow, is due the following Friday, and you will be working at a disadvantage relative to your classmates until you have access to the textbook--you might make friends with someone who does have the textbook.  Maybe--it depends a lot on you and your basic level of preparedness to aggressively pursue other resources available to you, for example on the internet.

There are many calculus resources available to you on the web, if you aren't yet aware of the Khan academy lectures on calculus you should check it out; many people find it a useful supplemental tool and it's free.

But let me take this opportunity to discuss outcomes with everybody.  Meditate on the image below.  If you've ever taken a night drive in the desert you can guess the outcome.  This calculus class is very much like that truck.  I guarantee that you are not faster or tougher than that truck.  That truck does not care how cool you are, or how good looking or how smart or how sneaky or how deserving you are.  After that truck there is another one.  The only way for you to survive this course is to take decisive action early and as often as necessary.  Otherwise I'll be feeling bad for you when I come to assigning grades at the end of the semester.

The first student question, answered here!

Good Afternoon Professor,

I just had a quick question concerning your book required for MAT 267.  I have the Calculus ASU book by James Stewart from 2013 (second edition I believe).  I was wondering if I could just use this book for your class instead of buying a new calculus book from the book store?  Thanks!

Very Respectfully,

**************

Sorry, the ISBN on my current book is 9781285100715 

The textbook for the course is listed on the course syllabus.   You asked this question before I announced the course syllabus, though and if would be useful for me to give a more detailed answer anyway, so here goes.  The textbook listed in the syllabus is Essential Calculus , Early Transcendentals by James Stewart, Thomson (Brooks/Cole), 2e,  which I believe is this one.  Notice that the ISBN of this text is different than the one you mention.  I can't really tell however, if the textbook you mention will do the job.  I suspect not: but you may wish to compare the sections that the syllabus says we will cover to the same sections of a new textbook owned by a classmate.

Hello, Happy Calculus Campers!  Welcome to my Calculus MAT 267 class,  Section 72767.  Our classroom is CDN#68 (College of Design North).  Your first homework assignment will open on this Friday August 21 at Noon and will be due the following Friday August 28 at 11:59PM.  You can use the "email instructor" button on the homework website to email me question you may have about the problems.   You should use the "Follow by Email" widget to the right to get notification of updates to this blog.