Geometry Question

Discussion in 'General Discussion' started by Alpha Prime, Nov 8, 2006.

  1. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    Ok, in geometry the altitude of a triange is ALT^2=b1*b2. Right?

    Ok then, if you have a triangle with a b1=5 ft and a b2=5 ft, the ALT=5 ft. Right?

    Ok, let's say i have a triangle that is isiolies (2 congruent side) with a b1 of 5ft and a b2 of 5ft and the congurent side are 28 ft. Alt= 5, using the formula at the top.

    And let's say i have another triangle that's is isiolies (2 congruent side) with a b1 of 5ft and a b2 of 5ft and the congurent side are 400 ft. Alt= 5, using the formula at the top.

    Why dosen't this formula give me the right answer? thanks in advance!
     
  2. tikgnat

    tikgnat Baweepgranaweepninnybong. TFW2005 Supporter

    Joined:
    Jul 2, 2002
    Posts:
    23,698
    News Credits:
    2
    Trophy Points:
    422
    Location:
    Beneath the Loft, London, UK
    Likes:
    +1,618
    Ebay:
    Twitter:
    Uh, this would be easier if you posted a picture of the problem.
     
  3. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    [​IMG]

    Sorry, had to scan it in. 'this help?
     
  4. Omegatron

    Omegatron Mandatory Fun. Buy it now TFW2005 Supporter

    Joined:
    Jun 29, 2004
    Posts:
    8,092
    News Credits:
    10
    Trophy Points:
    262
    Likes:
    +11
    Ebay:
    Your formula is not correct. That's the problem.

    To find the length of the altitude to a particular base of a triangle, multiply the length of one of the sides by the cosine of the angle that the side forms with the base.

    If you know the area of the triangle, multiply that area by 2 and divide by the length of the base to get the altitude.

    -Tony!
    Minored in math.
     
  5. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    that works if you have the angle but say you only have the informtion given.
     
  6. undertaker

    undertaker Deadman's Disciple

    Joined:
    Jan 23, 2004
    Posts:
    851
    Trophy Points:
    156
    Likes:
    +0
    It's been a while since I took geometry, but I think that formula of altitude^2 = b1*b2 only applies to right triangles with the hypotenuse as the base of the triangle. The formula won't work on all triangles in general. [It can't work in general. Test it on an equilateral triangle with side lengths of 2. The formula would say the altitude has length one, but the altitude would really have a length of square root of 3 (which you can determine with the Pythagorean theorem).
     
  7. Phy

    Phy I want... ROOM SERVICE!!

    Joined:
    Dec 10, 2005
    Posts:
    2,766
    News Credits:
    1
    Trophy Points:
    186
    Likes:
    +1
    It's the wrong formula. Y'oughta be using Pythagoras' theorem, from what I'm seein'.
     
  8. Fairy Princess

    Fairy Princess Banned

    Joined:
    Mar 21, 2004
    Posts:
    4,331
    Trophy Points:
    186
    Likes:
    +0
    Me I'd just post the problem on a web forum and let someone else solve it....







































    .... wait.
     
  9. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    I've been messing with it all day and i agree it only works on right triangles. So what is the formula for the height of a triangle? (i know it's simple, but i can't remember it)
     
  10. Boggs6ft7

    Boggs6ft7 TFW2005 Supporter

    Joined:
    May 25, 2006
    Posts:
    2,399
    Trophy Points:
    216
    Likes:
    +0
    for the side with a congruent side of 28, y can be solved by taking 28^2 - 5^2 = x^2. Solve for x. x = 27.5

    that's If you are allowed to use pythagorem(sp?), seems like the easiest way
     
  11. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    Ok thanks for all the help so far. The therom to find the alt of a scalene triangle is called Heron's Terom, whisch is crazy long.

    But, i still need to know how to find the length of the altitude in an isoselies triangle, and thankz again!
     
  12. Boggs6ft7

    Boggs6ft7 TFW2005 Supporter

    Joined:
    May 25, 2006
    Posts:
    2,399
    Trophy Points:
    216
    Likes:
    +0
    Well you could modify pythag by saying, the ALT = sqrt(Leg^2 - (base/2)^2)

    I don't know if there is a therom for that, I'm just using Trig
     
  13. llamatron

    llamatron Shut up, Nigel. TFW2005 Supporter

    Joined:
    Jul 11, 2002
    Posts:
    8,970
    News Credits:
    9
    Trophy Points:
    262
    Likes:
    +13
    Both of those triangles you drew can be broken up into right angle triangles. Then simply observe:

    [​IMG]

    You've provided enough information in that scan to solve for the height of both triangles.
     
  14. Omegatron

    Omegatron Mandatory Fun. Buy it now TFW2005 Supporter

    Joined:
    Jun 29, 2004
    Posts:
    8,092
    News Credits:
    10
    Trophy Points:
    262
    Likes:
    +11
    Ebay:
    Exactly. If you have an isoceles triangle where you know the length of the congruent sides and the length of the base, you can use Pythagorus to find the altitude. If S is the length of one of the congruent sides, and B is the length of the base, and A is the altitude, then A^2 + (B/2)^2 = S^2. Solving for A results in A = \|(S^2-[B/2]^2). (Using my crappy text, ' \| ' means 'the square root of' the quantity following in parantheses.

    -Tony!
     
  15. Alpha Prime

    Alpha Prime Ten Years Strong

    Joined:
    Apr 17, 2006
    Posts:
    1,192
    Trophy Points:
    176
    Likes:
    +0
    that's what i'm looking for, thanks Tony!
     
  16. Omegatron

    Omegatron Mandatory Fun. Buy it now TFW2005 Supporter

    Joined:
    Jun 29, 2004
    Posts:
    8,092
    News Credits:
    10
    Trophy Points:
    262
    Likes:
    +11
    Ebay:
    You're welcome. That'll be $7.50. :) 


    -Tony!
    Cheapest tutor on the net.
     

Share This Page