You are Here: Home >< Maths

# M2 Help Needed

1. The perpendicular unit vectors i and j are in the horizontal plane and the unit vector k is directed vertically upwards.

Write down the first two values of t for which Tom is directly below his starting
point.

Here is what I did:
The i and j components must be 0, so

Now I cant get a value of t in which both are 0, let alone a value for which bot are 0 and the K component is negative.

Help is highly appreciated

Edit: The MS says that the answers are t = 2pi and t= 4 pi. But putting t=2pi in gives r = 2i + 3.7k, which can't be directly below his starting position as it has moved 2 units east and 3.7 units up ?? And the same problem occurs when t=4 is put in.
2. hint: when t = 0

i = 2
j = 0

3. (Original post by a.partridge)
hint: when t = 0

i = 2
j = 0

But I need i = 0, j = 0 and k to be negative.
4. (Original post by member910132)
But I need i = 0, j = 0 and k to be negative.
well no value exists where cos(t) and sin(t) are both 0

but that doesn't matter because at the starting point (i) and (j) are not both 0.

the starting point comes from r(0) = ........ you see not the origin!
5. regarding the negative you can see that the solutions must be the first to satisfy the inequality

(A)t > 10 there A is the coefficient in the expression for the displacement parallel to K
6. (Original post by a.partridge)
well no value exists where cos(t) and sin(t) are both 0

but that doesn't matter because at the starting point (i) and (j) are not both 0.

the starting point comes from r(0) = ........ you see not the origin!
Thnx a lot for that

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 17, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### A-level exams coming up?

Find everything you need here.

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams
{"found_math": false, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "url": "https://www.thestudentroom.co.uk/showthread.php?t=1974898", "fetch_time": 1493495227000000000, "content_mime_type": "text/html", "warc_filename": "crawl-data/CC-MAIN-2017-17/segments/1492917123560.51/warc/CC-MAIN-20170423031203-00476-ip-10-145-167-34.ec2.internal.warc.gz", "warc_record_offset": 963636933, "warc_record_length": 38154, "token_count": 672, "char_count": 2515, "score": 3.703125, "int_score": 4, "crawl": "CC-MAIN-2017-17", "snapshot_type": "longest", "language": "en", "language_score": 0.9535863995552063, "file_path": "/sailhome/yjruan/project/latent-lm/data/processed/finemath-4plus/finemath-4plus/train-00056-of-00064.parquet"}