absolute values and magnitudes

Hi Dr. Taylor, I'm just wondering if on the last portion of the problem if
|w| is really supposed to be ||w|| since vectors don't technically have
absolute values

************
We discussed this in class: technically yes, you're a little bit right.  It's a common usage to write |w| instead of ||w|| for the very reason you mention: there's no such thing as the absolute value of a vector, so what else could  |w| mean but ||w||.  There's really no room for confusion so no harm in this usage.

10.3#5

this:
I am not sure where i have made my mistake on this problem, i took the
cross product of the vectors given <1,1,0>x<0,1,-5>  which gave me the new
orthogonal vector <-6,5,1> but since this problem needs the orthogonal
vector to have an i component that is equal to 1, i divided the 5 and 1 by
-6 getting the resultant vector <1,-5/6,-1/6>. Web work is saying that this
answer is incorrect. Is my set up wrong? Is the method for finding the
answer different that what i am attempting?
and this:
in response to the previous email, my set up was right, i ended up making a
small computational error while doing the cross product, i should have
equalled -5 not -6, throwing my answer off. Ended up getting the right
answer.

*************
Glad you figured it out on your own, this is the best possible outcome, especially because you learn to catch your own algebraic and arithmetic errors.

10.4#8

Hello Dr. Taylor!

I got the answer correct by finding the cross product of
the two vectors, then finding the ((magnitude of the cross
product)/(distance between Q and R)). Could you explain why this works
though? I would've thought it would have something to do with projection.

Thanks!

*******************
Oh. Yeah, I never thought about that, but you can do that.  Here's a picture of the points Q,R,P:

There is a dotted line passing through the two points Q, R, and a displacement vector from Q to P.  Notice that I've drawn a right triangle, one corner of which is at Q, the other corner at P, and the right angle on the line passing through Q and R.  I suppose that when you say "the two vectors" you mean the displacement vectors u=R-Q and v=P-Q.  Note that the hypotenuse of the triangle is ||v||. Then the part of v along the direction of  u  is (u.v)/(u.u) u, this is the displacement vector that goes from Q to the place where the blue line intersects the line QR, and has magnitude ||v|| Cos(θ) where θ is the angle RQP.  Of course a little trigonometry tells you that the opposite leg of the right triangle must have magnitude ||v||Sin(θ) = ||uxv||/||u||

10.3#11

Dear Dr. Taylor,
I am a little confused about what I am doing wrong.  I
have been using the equation W=|F||D|cos(Theta) and received the answer
(31sqrt(3))/2.

Thanks,

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

You meant 3*1*sqrt(3)/2.  That kind of mistake will kill you on the exam though, so be careful.

10.2#10

Hi, I'm not sure if you can see my attempts for this problem but I've done
it a bunch of times and I can't figure out where I am going wrong with the
second part to this question. If you could give me a little guidance I
would really appreciate it thank you!

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

Well, you got the speed right.  The angle is a mistake of course.   It's interesting though because, although it's close to the correct answer in an absolute sense, the relative error is about 10%.  I went through the usual list of mistakes people make in computing angles and they all gave smaller relative errors than that, so I really can't imagine how you got that answer, except maybe bad arithmetic or a typo. For instance using 13 instead of 14 would give about the answer you have. 

 

To reiterate a comment I made in an earlier post, when you submit a question like this you need to tell me what you tried so I can catch your mistake. 

Yes I can see how many times you tried to do the problem. So as far as guidance, just flailing and trying lots of guesses isn't going to help you. Stop doing that.  Stepping back and making sure you understand the math, and making sure you did the steps correctly will work better than that 

Lecture Notes 8/28/17 through 9/1/17 (complete!)

Lecture Notes 8/28/17

Lecture Notes 8/30/17

Lecture Notes 9/1/17

10.3#14

Mr. Taylor,

I just don't understand this question at all, and as you can

probably see I've tried it a ton of different times

Thank you for any help

**************************Well you clearly do understand something since you got the a) correct.  It *looks like maybe* you tried to do part b) correctly too, except you made a wee little mistake subtracting the one vector from the other.  I can't tell though, because *you didn't tell me what you did*.  May I suggest that you do that when send me a question?--it usually is a better teaching moment if I can tell you exactly where you made a mistake.   BTW, we used exactly the terminology this vector parallel and that vector perpendicular in the lecture notes from last Wednesday and/or Friday, and those lecture notes are already posted here in the blog, and this stuff is also discussed in section 10.3 in the textbook.  I didn't lecture on the stuff about work, but is also discussed in the textbook in glorious detail.  The upshot is that the work is defined  as the Force vector dot product with the displacement vector.

10.3#19

I've been working on a problem, specifically number 19. I keep getting
sqrt(78),sqrt(26). But the problem says I'm getting it wrong. I also had a
friend attempt the problem and he got the same thing as me, yet still
wrong. It is asking for the length of the diagonals using u=<-3,2> and
v=<7,4>. Any help on why it says it's wrong?

Thanks,

****************
Well the answers you have now are different and correct so it looks like you figured it out.

10.2#13

Dear Mr. Taylor,
I just wanted to clarify how many tries we are supposed
to get when completing homework.  While working through the homework, this
problem seems to have given me a limit to the number of tries before
marking it wrong.

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

OK, I changed the problem to allow unlimited number of attempts.  But before you go, let me point out that the reason 10.2#13 had limited number of attempts is because it was a lot of True-False problems, and it is not too difficult for *someone* without even understanding the problem to just go on guessing until they guess all correct answers and then walk away giving themselves a pat on the head for that.  This would be a *bad mistake* because they would have failed to understand what the problem was about, which would mean that that basic understanding would not be available, come all those difficult and scary exams that will come.  The fact that you bumped into the attempt limit means that you were trying to do the problems without understanding the material, when you should make sure that you understand the material before you try the problem, and certainly before you've tried the problem three or four times.  I suggest that you should attend my office hours or otherwise get tutoring before you get to that point.

10.3#9 frustration

Hi Professor,

I have been working on 10.3 problem 9 for quite some time now and am almost 100% positive the answer I have placed for y is correct. Please let me know if there is something wrong with the grading or if I am doing it incorrectly?

Thank you,

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

First of all, when you have a question about the webwork, could you *please* ask it by clicking the "Email instructor" link at the bottom of the page--you can send exactly the same message but the software will send me the same image as your screenshot above, but will also give me access to the problem as you worked it and in addition computer code that is behind your webwork problem so that I can check it for bugs.

Your answers above are correct to two decimal places.  My *hypothesis* is that webwork is being finicky about wanting three decimal places--that's often the case when this happens, but occasionally there is a bug in the code instead.  If you send do the email instructor button I'll check it out and update this post. 

Lecture Notes 8/21/17 through 8/25/17(complete!)

Lecture Notes 8/21/17

Lecture Notes 8/23/17

Lecture Notes 8/25/17

No homework Friday 8/25/17 and yes homework 9/1/17

Hi Dr. Taylor,

Will the 10.3 and 10.4 webwork assignments be due next Friday as originally posted? I know 10.1 and 10.2 were moved to that date.

Thanks,
**************
Depends on if we do section 10.4 tomorrow.  It's looking highly likely though.

MAT 267 homework site down (Uh, no)

Dr. Taylor,

I'm assuming you won't receive this until the morning, but I was wondering if the WeBWorK site is also down on your end. I've had it bookmarked since last week but now I'm getting an error when I try to access it. 

Thanks,

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

I'm not sure if it was down when you sent this message, but the most common cause of this problem is that your login certificate to ASU is expired.  You need to have a current active login to ASU, e.g. myasu, to be able to access the webwork. If in doubt reload your myasu, and then if you have to login again reload the webwork **after** deleting everything to the left of the question mark in the URL bar

10.3#17

Good evening Dr. Taylor,

I am having trouble figuring out what the dot
product would be when looking at a graph; I realize that parallel and
orthogonal vectors would have a dot product of zero, but I can't tell when
two vectors would be positive or negative.

Thank you!
*****************************

ok, here's your hint.  the trick to this problem is exactly what we discussed in class on wednesday:

u.v = ||u|| ||v|| cos(θ)

Since u.v can be positive only if all of ||u|| ||v|| cos(θ) are positive, and can be negative only if both of  ||u||, ||v|| are positive (since they can't be negative) while cos(θ) is negative.  Looking at the vectors in the image, they are each clearly not the zero vector, hence in each case ||u||, ||v|| are positive. This means that the answer to all of these questions depends only on cos(θ).  So you can know everything you need to know by eye-balling the angles between each pair of vectors and knowing about the properties of cos(θ).  (NOTE: go study cos(θ))

Office Hours

The MAT267 Office Hours will be:
Mon 12:30-1:30
Wed 1:30-2:30
Friday 2:30-3:30

A couple of comments.

1) This schedule manages to accommodate 55 of the 61 people (which is less than half of the students taking calculus from me) who had answered the poll.

2) If you can't make my office hours, scheduling a meeting with me is always an option for you.

3) You are telling me that you will come to an office hour on Friday afternoon.  We'll see.  If attendance is very low I reserve the right to reschedule that time to one more convenient.

Office hours poll

Hi All, please give your office hours availability in the doodle poll at the following link:
<https://beta.doodle.com/poll/p5sgf7n34db24wf7>
Instructions: please click on every available time slot for which you could attend the office hours for at least 15 minutes out of the hour.
thanks!
--Tom Taylor

RE WebAssign

On Fri, Aug 18, 2017 at 11:55 AM, ************   wrote:

is web work different from web assign. I'm curious because the book list said to purchase web assign so I purchased the text book new. however if I do not need web assign ill return it and get a used copy. will all homework be done through web work and do I need to purchase it ?

*******************************
To quote from line 6 of the syllabus:

Text: Essential Calculus , Early Transcendentals by James Stewart, Thomson (Brooks/Cole), 2e (Or, if you are on campus and want to look in the bookstore, the book designed for ASU and has a hand on the front cover is: ACP Calculus (Custom) ASU Bundle (w/Enh WebAssign Access) We will not use WebAssign but the price of the text with it is the same as the price without it.)

Welcome to MAT267, and some useful information

Hi All, welcome to your MAT267 blog. You can look here to find assignments, posted scores & estimated grades, questions and answers. I suggest that you bookmark this page, and also subscribe to email updates to this blog in the subscription field to the right.

1) Your Posting ID. Your Posting ID will be used to identify your scores. You should not share your Posting ID or do anything to compromise it's security. To quote from this link:

Posting ID
Your Posting ID is a seven-digit number composed of the last four digits of your ASU ID number plus the last three digits of your Campus ID number, separated by a hyphen. Your Posting ID is printed on the class rosters and grade rosters your professors work with. You can also view your Posting ID on the My Profile tab in My ASU.

2) For that matter, especially don't do anything to compromise the security of your ASU or Campus ID numbers--they can be used to for identity theft or invade your privacy. For instance, DO NOT SEND MY YOUR ID'S BY EMAIL--I don't need them to interact with you and email is an inherently insecure form of communication.

3) The first homework assignment is sections 10.1 and 10.2, which due on Friday August 25 at 11:59 PM.