1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

A Trig Question

Discussion in 'Off Topic [BG]' started by rarbass, Sep 18, 2010.


  1. rarbass

    rarbass

    Jul 3, 2008
    A triangle has three sides, 1.6m, 1.9m and 0.32m.
    What are the three angles within the triangle?

    We have the answer, but apparently my math skills aren't working for such a basic question.

    Could someone do this question and provide your steps as well?

    I thought I knew how to do this, but apparently my answer doesn't match.
     
  2. oldrocker

    oldrocker Supporting Member

    Feb 13, 2005
    Long Island, NY
    Not sure - but I bet they add up to 180
     
  3. rarbass

    rarbass

    Jul 3, 2008
    Yes of course, but the problem is that we aren't given any angles to start with.

    My thought was to plug all the given sides into the cosine law, and do inverse cos at the end to find the angle (then repeat for the other angles) however our answers always end up wrong.

    I've been through 2 university calculus courses, yet this just isn't working for me. (trying to help someone)
     
  4. 18.612 deg
    157.727 deg
    3.66 deg

    using law of Cosines

    A² = B² + C² −2(B)(C)cos(angle 1)
    B² = A² + C² −2(A)(C)cos(angle 2)
    C² = A² + B² −2(A)(B)cos(angle 3)

    A,B and C being the lengths of the sides
     
  5. nutdog

    nutdog when I'm a good dog they sometimes throw me a bone Supporting Member

    Feb 19, 2009
    in the dog house
  6. That works too...
     
  7. rarbass

    rarbass

    Jul 3, 2008
    That is exactly what I did, I just felt that 3.66 was a bit far from the given solution of 3.3.

    The given answers are:
    3.3
    158.1
    19.5

    See? We got the same answers as you, so why are their given solutions all off? Would the professor do this on purpose, or how else could the given solutions be that far off?

    Thanks a lot for helping out!
     
  8. nutdog

    nutdog when I'm a good dog they sometimes throw me a bone Supporting Member

    Feb 19, 2009
    in the dog house
    I'm too lazy to do it. And it would give me really bad flashbacks.
     
  9. ah yes...me too..too many years since I got my EE. We did all this stuff on a slide rule back then. Boy, I'm dating myself now :atoz:
     
  10. Buchada Azeda

    Buchada Azeda

    Mar 25, 2009
    Brazil
    I love math, but trigonometry is the single worst thing to learn in school. I just can't stand it.
     
  11. nutdog

    nutdog when I'm a good dog they sometimes throw me a bone Supporting Member

    Feb 19, 2009
    in the dog house
    Because there is no truth. One answer is as good as another. And I see you're in Canada. Maybe that's it.
     

  12. maybe the prof is trying to throw you off to prove him wrong...I had a circuits analyses prof do that a few times, just to see if we were on our toes...

    Math is either right or wrong...if you and I came up with the same answer irrespective of each other, then I would say the prof is wrong :eyebrow:
     
  13. I must be a sucker for pain...I loved trig. I hated probability and statistics...I used to call it "unmath". To many variables and unknowns for me to be called "real" math...
     
  14. nutdog

    nutdog when I'm a good dog they sometimes throw me a bone Supporting Member

    Feb 19, 2009
    in the dog house
    trig OK. linear algebra--aaaaaaaaahhhhh!
     
  15. rarbass

    rarbass

    Jul 3, 2008
    This is possible. I think maybe he might just be trying to make them 100% confident in their math skills so they won't feel the need to check their answers.

    Personally I dont agree with that, you're trying to learn the material and I've always found that having the answers present allows me to confirm that I'm actually learning and not just guessing. But hey it's not my program.
     
  16. rarbass

    rarbass

    Jul 3, 2008
  17. Draw a picture of it. But scale it down to centimeters or something. I could do it in AutoCAD if I had AutoCAD at my fingertips, but I'm on my MacBook.
     
  18. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
  19. funkydjembe

    funkydjembe

    Apr 5, 2007
    Norway
    all angles=180 degrees. 1.6+1.9+0.32=3.82
    180 divided by 3.82= 47.1020419blah
    47.1 times 0.32=15.08
    47.1 times 1.6= 75.4
    47.1 times 1.9=89.53

    took a quick chance on this,,,any doubts?
     
  20. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    That won't work - the ratio of the angles is not just the ratio of the sides. Consider the pythagorean triad 3, 4, 5. The side opposite the right angle would be exactly half the perimeter if your method worked; clearly this is not the case.

    Given 3 sides of a triangle, you use the cosine rule to work out the biggest angle and then the sine rule to get one of the other two angles. Then get the final angle by subtraction from 180.
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Mar 5, 2021

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.