Results 1 to 13 of 13

Thread: math help for my teacher

  1. #1
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default math help for my teacher



    Find the radius, the perimeter(solid blue) is 25.

    I'm TA for my old math teacher, and he asked me to find out the answer to this for his honors geometrey class, just for old times sake(we always used to do these little challenges), and this time i'm stumped. He also doesn't know how to do this, so he has me, and every other math teacher working on this. I figured you guys are smarter
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

  2. #2
    Join Date
    Sep 2006
    Location
    Canada
    Posts
    1,124
    Mentioned
    0 Post(s)
    Quoted
    5 Post(s)

    Default

    does p = the inscribed angle?

    It looks like you made it go a little past it, but it's possible you were just being sloppy.



  3. #3
    Join Date
    Jul 2010
    Posts
    1,115
    Mentioned
    1 Post(s)
    Quoted
    10 Post(s)

    Default

    perimeter i believe

  4. #4
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default

    Quote Originally Posted by Capricorn View Post
    does p = the inscribed angle?

    It looks like you made it go a little past it, but it's possible you were just being sloppy.
    p = entire perimiter excluding dotted line, yes i was being sloppy
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

  5. #5
    Join Date
    Jul 2010
    Posts
    1,115
    Mentioned
    1 Post(s)
    Quoted
    10 Post(s)

    Default

    radius is about 4.224. diam is 8.448
    to figure it out start with .5 pi X + sqrt (X^2 -49) + 7 = 25
    eventually you get X = 8.448ish. from there you test by plugging it in for X.
    8.448 pi / 2 + 7 + sqrt (( 8.448^2 )-( 7^2 )) (which gives you your your other leg of 4.729) = 25 almost exact.

  6. #6
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default

    could you post a source of the formula/ website where i can learn how,

    it looks right, but i need to make sure + understand all of it
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

  7. #7
    Join Date
    Jul 2010
    Posts
    1,115
    Mentioned
    1 Post(s)
    Quoted
    10 Post(s)

    Default

    i used pathagorean. but started off with half of circumference plus the two sides = 25 (perim). from there its algebra

  8. #8
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default

    /facedesk

    i can't beileve i havn't seen this D:

    thanks for the help
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

  9. #9
    Join Date
    Jul 2010
    Posts
    1,115
    Mentioned
    1 Post(s)
    Quoted
    10 Post(s)

    Default

    yeah

  10. #10
    Join Date
    May 2006
    Posts
    151
    Mentioned
    0 Post(s)
    Quoted
    0 Post(s)

    Default

    Well.. here's how I did it (finally without errors...):

    Call the unlabeled side of the triangle x (the one that's not the diameter of the circle)
    then the perimeter 25 = PI*r + 7 + x
    PI * r = 18 - x -- rearranging
    2r = (36 - 2x) / PI -- 2r is the length of the hypotenuse of the triangle.

    7^2 + x^2 = (36/PI - 2x/PI)^2 -- By Pythagoras

    .. do some algebra to get ..

    -0.594x^2 - 14.6x + 82.3 = 0 -- (note: these are rounded here but not for calculating answer)

    x = 4.72975 -- solving and using the sensible answer for x (other answer is negative)

    r = (18 - 4.72975) / PI -- substituting into earlier equation
    = 4.22405 rounded to 5 d. p.

    Is "honours" something you do at high school? or where?

    EDIT: Just realised radius of 3.5 doesn't make sense based on the problem... sorry!
    EDIT2: Fixed. Some errors in my algebra
    Last edited by any_one; 04-15-2011 at 04:42 AM.

  11. #11
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default

    honors is just the normal highschool class, but a little more intence(students actually care about the subject, want to be challenged).
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

  12. #12
    Join Date
    May 2006
    Posts
    151
    Mentioned
    0 Post(s)
    Quoted
    0 Post(s)

    Default

    Oh, that's cool I did a year ahead in maths in high school also.. Finally got a sensible answer after making some silly mistake in the algebra twice -_- I'll edit my post above. It's the same as bolshak, r = 4.22405

  13. #13
    Join Date
    May 2007
    Location
    knoxville
    Posts
    2,873
    Mentioned
    7 Post(s)
    Quoted
    70 Post(s)

    Default

    I was also ahead a year, I havent took the class in two years
    <TViYH> i had a dream about you again awkwardsaw
    Malachi 2:3

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

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