Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 28
  1. #1
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Law of cosines is defeating me :(

    aaah this is hard. These law of cosine things, sheesh they make an equation too large for my to handle i dont know where to start . Anybody have any hints?
    C://dos
    C://dos.run
    run.dos.run

  2. #2
    Specialized Member ChAnMaN's Avatar
    Join Date
    Nov 2003
    Location
    I live in a small town
    My Bikes
    2004 Specialized Allez
    Posts
    973
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    could you elaborate alittle more on what equations your talking about?
    You can never be too Specialized
    Click here if any of the following apply to you:
    1 You dont like Specialized, 2 You drive a SUV, 3 Your name is George Bush

  3. #3
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    certainly. Infact i will draw out the problem in autocad or something
    C://dos
    C://dos.run
    run.dos.run

  4. #4
    Permanent Amateur Mark B10Cycle's Avatar
    Join Date
    Dec 2004
    Location
    Richmond, VA
    My Bikes
    Specialized Allez, Nishiki MTB
    Posts
    349
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I just did this in school myself. I'll be the first to tell you I'm not a math guy, but if you can explain the problem a little more maybe I can help.

    Are you having a problem with the formula or its application?
    I may be going to hell in a bucket, babe,
    But at least I'm enjoying the ride.

    -The Grateful Dead

  5. #5
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    alright im doing a quick drawing in paint
    hold on (5 minutes)
    C://dos
    C://dos.run
    run.dos.run

  6. #6
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)


    AAAAH.
    C://dos
    C://dos.run
    run.dos.run

  7. #7
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    aaargh ive always hated math beyond multiplication, proofs, addition, subtraction and division but this....oooooooo this is beyond hate! Im so close to wanting to destroy something.
    C://dos
    C://dos.run
    run.dos.run

  8. #8
    Senior Member
    Join Date
    Feb 2004
    Location
    Cleveland, OH
    My Bikes
    2004 Trek 4600, 1980's Univega Supra Sport, 2006 Lemond Reno
    Posts
    2,287
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    If you look in your book, you should find a formula where you can use the sides to find the angles. Trig is the easier of the Algebra/Trigonometry/Calculus trifecta of higher math.

  9. #9
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    algebra sucked, but not nearly as bad as this. See heres the scoop, my math teacher is the biggest math geek i know. He teaches most of the higher math classes. Part of the geometry curiculum is a 4 day intro to the very basics of trig. This guy loves trig and not geometry. He always goes way beyond what is required and faster than any other class. SO we are 3 weeks ahead of the curiculum. So hes spending 4 weeks instead of 4 days . And i hate it already and its just been a week. Past precalc im not wanting to take any more classes of math.
    So far in engineering i have used only basic math and a fine calculator from texas instruments
    C://dos
    C://dos.run
    run.dos.run

  10. #10
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    and my book is a geometry book, it only has the very bare stuff like cos sin tan stuff
    C://dos
    C://dos.run
    run.dos.run

  11. #11
    Senior Member sewupnut's Avatar
    Join Date
    Jan 2005
    Location
    Mountains and Plains of Colorado
    My Bikes
    Seven Odonata, Trek 950, 86 Stumpjumper, MASI 3V, Schwinn LeTour
    Posts
    168
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I'd look for a different vocation. Lot's of math in engineering - especially calculus.
    2nd semester calc, you gotta know trig cold.

    sun

  12. #12
    Senior Member
    Join Date
    Feb 2004
    Location
    Cleveland, OH
    My Bikes
    2004 Trek 4600, 1980's Univega Supra Sport, 2006 Lemond Reno
    Posts
    2,287
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    is this supposed to be a right triangle?

  13. #13
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I see myself with a mighty TI89, the calculator thats banned from DHS math dept. but who gives a rats petoot in the eng lab . *sigh* but i guess im gonna end up taking all this crap anyways despite how much i hate it. Its the one class this year I have to work at with effort and im a lazy person, not a good blend
    C://dos
    C://dos.run
    run.dos.run

  14. #14
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    its not supposed to be a rt triangle
    C://dos
    C://dos.run
    run.dos.run

  15. #15
    Senior Member
    Join Date
    Feb 2004
    Location
    Cleveland, OH
    My Bikes
    2004 Trek 4600, 1980's Univega Supra Sport, 2006 Lemond Reno
    Posts
    2,287
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by phantomcow2
    its not supposed to be a rt triangle
    You're f***ed then.

  16. #16
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    i wish it was a rt triangle, i can solve those like a machine . He said something about making an imaginary line from the apex of the triangle down, so that it meets the base at a 90 degree angle and calling that segment h. Then applying law of cosines to find the sides or something. aaah the more i think about it, the more i get confused
    C://dos
    C://dos.run
    run.dos.run

  17. #17
    cab horn
    Join Date
    Jun 2004
    Location
    Toronto
    My Bikes
    1987 Bianchi Campione
    Posts
    28,292
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Aw come on. This stuff you should know like the back of your hand. Just practice a bit more.

  18. #18
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I just started it so i dont know. He taught us law of cosine and sine friday and said "here, do this for homework" I wish i knew it, im at a stall though i have no idea what to do
    C://dos
    C://dos.run
    run.dos.run

  19. #19
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    and to add to the fun, he said if we dont have it done we have an hours detention.

    pffft...screw that, i did work and thats good enough
    C://dos
    C://dos.run
    run.dos.run

  20. #20
    So say we all.
    Join Date
    Nov 2004
    Location
    Austin, TX
    My Bikes
    Gary Fischer Wahoo, upgraded Specialized Allez
    Posts
    728
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Law of cosines -- no worries. It's GREAT, it's EASY and you don't have to worry about making sure you're dealing with a fracking right triangle.

    You know Pythagorean theorem: c^2 = a^2 + b^2? That's easy. That's for right triangles. Law of cosines is the SAME THING without having to worry about it being a right triangle!
    c^2 = a^2 + b^2 - 2ab cos angleC
    If this were a right triangle, then the angleC would be 90 degrees, and you'd get the Pythagorean theorem. The 2ab cos angleC is the "fudge factor" that lets you adjust for the non-rightedness of the triangle.
    Seriously, it's that easy. You know the Pythagorean Theorem. So use it. Then all you have to remember is that if your angle C isn't 90 degrees, if you're not playing with a right triangle, you have to subtract 2 * a * b * cos Cangle.

    If you read nothing else, read this:
    MOST MATH TEACHERS DON'T TELL YOU HOW TO KNOW WHEN TO USE ALL THEIR STUPID FORMULAS. This is an engineer who learned the hard way.
    You need a cheat sheet. Not for tests, but for doing your homework. Write down all the formulas in the unit, then right by them write what they're good for. Here's a quick one.

    Pythagorean theorem. c^2 = a^2 + b^2. Rt. triangle, use lengths of 2 sides to find length of 3rd
    Law of sines a/sin A = b/sin B = c/sin C = 2R Any triangle, relationship between size of angle and length of it's opposing side
    Law of cosines: (above) : length of all 3 sides and size of one angle: find whichever one's missing.

    So you use the law of Sines and law of Cosines together a lot. Like in your homework -- you have the length of all 3 sides and you need to know the angles. Check your cheat sheet -- you can find ONE angle with the law of cosines. So then you've got that angle. Now you need other angles. You can use the law of cosines again -- chug through -- or you can check the law of sines. Your cheat sheet says "relationships between side lengths and angles" and you KNOW the side lengths, and you know ONE angle. So one of the entries in the equal sign series is a number you can find. So you can use it to find the rest.

    So math isn't hard, it's just frequently taught crappily. Formulas are just tools. Equal signs are just equal signs. I could multiply both sides by a million if I wanted to, but it wouldn't be useful. Formulas and theorems like this are just tools to use when you want to do something useful. If you've got a bike with a pedal attached and you want to take it off, use a pedal wrench. If you've got a triangle with all the side lengths and you want to know an angle, use the law of cosines. It's not as mechanical and easy to see, but after you get the trick it's not a problem. It's like seeing one of those "magic eye" pictures -- after it clicks it's much easier to get the next one.

    Good luck.
    PS: Engineering sucks though.
    /Engineering grad student

  21. #21
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by RedHairedScot
    Law of cosines -- no worries. It's GREAT, it's EASY and you don't have to worry about making sure you're dealing with a fracking right triangle.

    You know Pythagorean theorem: c^2 = a^2 + b^2? That's easy. That's for right triangles. Law of cosines is the SAME THING without having to worry about it being a right triangle!
    c^2 = a^2 + b^2 - 2ab cos angleC
    If this were a right triangle, then the angleC would be 90 degrees, and you'd get the Pythagorean theorem. The 2ab cos angleC is the "fudge factor" that lets you adjust for the non-rightedness of the triangle.
    Seriously, it's that easy. You know the Pythagorean Theorem. So use it. Then all you have to remember is that if your angle C isn't 90 degrees, if you're not playing with a right triangle, you have to subtract 2 * a * b * cos Cangle.

    If you read nothing else, read this:
    MOST MATH TEACHERS DON'T TELL YOU HOW TO KNOW WHEN TO USE ALL THEIR STUPID FORMULAS. This is an engineer who learned the hard way.
    You need a cheat sheet. Not for tests, but for doing your homework. Write down all the formulas in the unit, then right by them write what they're good for. Here's a quick one.

    Pythagorean theorem. c^2 = a^2 + b^2. Rt. triangle, use lengths of 2 sides to find length of 3rd
    Law of sines a/sin A = b/sin B = c/sin C = 2R Any triangle, relationship between size of angle and length of it's opposing side
    Law of cosines: (above) : length of all 3 sides and size of one angle: find whichever one's missing.

    So you use the law of Sines and law of Cosines together a lot. Like in your homework -- you have the length of all 3 sides and you need to know the angles. Check your cheat sheet -- you can find ONE angle with the law of cosines. So then you've got that angle. Now you need other angles. You can use the law of cosines again -- chug through -- or you can check the law of sines. Your cheat sheet says "relationships between side lengths and angles" and you KNOW the side lengths, and you know ONE angle. So one of the entries in the equal sign series is a number you can find. So you can use it to find the rest.

    So math isn't hard, it's just frequently taught crappily. Formulas are just tools. Equal signs are just equal signs. I could multiply both sides by a million if I wanted to, but it wouldn't be useful. Formulas and theorems like this are just tools to use when you want to do something useful. If you've got a bike with a pedal attached and you want to take it off, use a pedal wrench. If you've got a triangle with all the side lengths and you want to know an angle, use the law of cosines. It's not as mechanical and easy to see, but after you get the trick it's not a problem. It's like seeing one of those "magic eye" pictures -- after it clicks it's much easier to get the next one.

    Good luck.
    PS: Engineering sucks though.
    /Engineering grad student
    thankyou thankyou thankyou .
    C://dos
    C://dos.run
    run.dos.run

  22. #22
    Permanent Amateur Mark B10Cycle's Avatar
    Join Date
    Dec 2004
    Location
    Richmond, VA
    My Bikes
    Specialized Allez, Nishiki MTB
    Posts
    349
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Like Scot said, C^2=A^2+B^2-2AB Cos<c

    So for you if you wanted to find say, <Gamma
    4^2=8^2+5^2-2*8*5*Cos<Gamma

    You'd carry out all that crap and work it down to isolate <Gamma

    Don't worry, I'm not a math guy myself in any way and I've managed to figure most of this out.
    I may be going to hell in a bucket, babe,
    But at least I'm enjoying the ride.

    -The Grateful Dead

  23. #23
    Evil Genius capsicum's Avatar
    Join Date
    May 2004
    Location
    Sumner, WA
    My Bikes
    '92 novara ponderosa, '74 schwinn le tour, Novara fusion, novara transfer, novara randonee(2), novara careema pro, novara bonita(2).
    Posts
    1,529
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    cosine is just the inverse of sine like if sine was 33/65 then cosine is 65/33(read 65 over 33). and sine is opposite side over hypotinuse I think wait forget that I'm too tired but I have a kick butt trig book that I got from a second hand store, after I was out of school, that made me go "Wow this is easy, the public school system really does suck as$."
    Then I was watching this education expert professer dude on the tele and he was like mathbooks in this country suck then as a good example he described european and japanese math books.
    Well that kickass book I got, it matches the description of the japanese and euro texts which is "readable, no masses of sidebars, bubbles, worthless trivia, random reveiw sections, or endless lists of problems" (like cramming it in harder with more problems is going to do any good when you don't understand it in the first place. Bigger hammer, the american way.) So the book is written so it can be read, now get this, like a book, real paragraphs and everything with an occational picture and problem as an example, and two or three practice problems at the end of the chapter. it covers a whole trig course, clearly, in about 120 6"x10" black and white pages.
    I'll get it out tomarrow and look up laws of sine/cosine tangent/cotangent secant/cosecant
    "Data is not the plural form of annecdote."
    "yuo ned to be deadurcated"

  24. #24
    Chronic Tai Shan ofofhy's Avatar
    Join Date
    Oct 2004
    Location
    PHL
    My Bikes
    '74 Fuji SRS
    Posts
    1,115
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by capsicum
    cosine is just the inverse of sine
    The inverse of sine is the arcsin =sin^-1.

    1/sin = cosecant = csc
    From Craig's List: IF its a singlespeed that means----all the other parts are broken cut off and dumped...dont buy singlespeeds, the bikes will make your balls fall off

    * no -- it's NOT ok to contact this poster with services or other commercial interests

  25. #25
    Senior Member joeprim's Avatar
    Join Date
    Jan 2002
    Location
    Northern Neck Tidewater Va.
    Posts
    1,688
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Redhaiedscott got it right, just thought I'd add a comment that might make the law of cos seem more familiar. You could use it for a rt. triangle because the cos(90) is 0 so the payth. therom is mearly a special case of the law of cos.

    To learn math you must calm down and just do lots of poblems. Any time you take a math class go buy the Schaum's Outline. After 40 years of engineering I still buy one once in a while if I need to learn something new (long ago tired of classes).

    Joe

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •