Math question!

• wrexham

  8 Jun 07, 23:45

  http://i106.photobucket.com/albums/m262/janepigeon/217_squarecircle.gif
  
  In the following diagram, each blue line is 24 centimetres long, and the red line is 16 centimetres long. Assume the shape in the centre of the circle is a perfect square, and it is exactly centred in the circle. Also assume that all three coloured lines are parallel to each other.
  
  What is the radius of the circle, in centimetres? Please round up to the nearest centimetre.
• MyPillowTalks

  8 Jun 07, 23:48

  
• tripudio_mutatio

  8 Jun 07, 23:49

  24cm?
• wrexham

  8 Jun 07, 23:50

  thanks pillow. was trying to do that
  
  hahaha. 24 cm. O.O why?
• wrexham

  8 Jun 07, 23:51

  osh1t -.- now i see it
  
  hahaha. stupid thread. thanks!
• Darkness_hacker99

  8 Jun 07, 23:52

  This question is at which level? O level? A level?
• Fog

  8 Jun 07, 23:52

  i only know that the side of the square is square root of 128. extend the red line such that it lies on the imaginary line which connects the 2 points of the blue lines in the square. then the diagonal of the square is (24-16) x 2 = 16. by pythagoras theorem the side of the square = square root of 1/2 (16^2) = square root 128 hope that helped if not never mind cuz i bo liao
• Fog

  8 Jun 07, 23:55

  Originally posted by Fog:

  i only know that the side of the square is square root of 128. extend the red line such that it lies on the imaginary line which connects the 2 points of the blue lines in the square. then the diagonal of the square is (24-16) x 2 = 16. by pythagoras theorem the side of the square = square root of 1/2 (16^2) = square root 128 hope that helped if not never mind cuz i bo liao

  SHIT I THINK TOO FAR. JUST EXTEND THE RED LINE UNTIL IT TOUCHES CENTRE OF CIRCLE AND THAT RED LINE WILL BE RADIUS OF CIRCLE WHICH IS 16 + 8 = 24. OMG
• teraexa

  8 Jun 07, 23:56

  EDIT: Wrong answer. See my 3rd post.
• Darkness_hacker99

  9 Jun 07, 00:00

  edited due to picture too big..
• teraexa

  9 Jun 07, 00:03

  Originally posted by Darkness_hacker99:

  Nah. I won't do your homework, but I can show you the steps.
  
  

  Hey dude, ur blue lines didnt start at the same 'line' as the red line.
  
  To illustrate my point, try connect the 3 points which the blue and red lines intersects the circumference.
  
  You will find that the resulting connection will be find a straight line (see thin line) due to the fact that it is a circle.
  
  
  
  As a result, we CANNOT assume that it is 16cm.
  
  *EDIT: Added pic to illustrate my point*
• Darkness_hacker99

  9 Jun 07, 00:04

  Originally posted by teraexa:

  Hey dude, ur blue lines didnt start at the same 'line' as the red line.
  
  To illustrate my point, try connect the 3 points which the blue and red lines intersects the circumference.
  
  You will find that the resulting connection will not find a straight line due to the fact that it is a circle.

  I just realized that my answer is wrong. hahaz.
• Darkness_hacker99

  9 Jun 07, 00:16

  
  
  I lose touch with the reality for awhile while doing this question..
• teraexa

  9 Jun 07, 00:24

  Don't worry. I nearly made that assumption while solving this question.
  
  Then I realised that I was wrong.
• zanza

  9 Jun 07, 00:24

  lol my method is logic based.
  
  To find the centre of a square, you draw a straight line from both corners, the point where they intersect is the middle of the square.
  
  since they said the square is perfectly centred on the circle, it would be safe to say that the centre of the square is also the exact centre of the circle.
  
  Take the distance, from the two poles( BLue Line ) and voila, radius
• Darkness_hacker99

  9 Jun 07, 00:28

  Originally posted by teraexa:

  Don't worry. I nearly made that assumption while solving this question.
  
  Then I realised that I was wrong.

  To err is human.. It's good to realize one mistake and never make them again.
• wrexham

  9 Jun 07, 02:48

  it's not my math HW lah -.- rofl
  
  school where got so lame one. colour code
  
  i where got so boliao. scan somemore. hahhaa
  
  ty for answers -.- all different though.
• Darkness_hacker99

  9 Jun 07, 02:51

  Originally posted by wrexham:

  it's not my math HW lah -.- rofl
  
  school where got so lame one. colour code
  
  i where got so boliao. scan somemore. hahhaa
  
  ty for answers -.- all different though.

  What's the model answer?
• the.owl

  9 Jun 07, 05:43

  use pythagoras lor.
• JRtheBEST™

  9 Jun 07, 10:19

  the question states the blue lines is parallel to the red and the other blue lin, if we exchange the blue line to be in the place of the red line, the RADIUS of the circle will be 24cm
• hiphop2009

  9 Jun 07, 10:21

  hey, next time post here: http://schoolwork.sgforums.com
• teraexa

  9 Jun 07, 23:00

  Eh paiseh I retract my previous answer after some checking up on the properties of chords in a circle.
  
  Basically, we make use of the property that the product of the segments of 2 intersecting chords are equal.
  
  See http://www.algebralab.org/Word/Word.aspx?file=Geometry_CirclesAnglesChords.xml question (i) for a worked example.
  
  So for this question, if we draw another blue line to one of the corner of the square, the length of the blue line will be 24cm. See my new image.
  
  
  
  Therefore using the above-mentioned property, (1) x (2) = (3) x (4).
  
  Let the diagonal of the sqaure be 2y, 24 x 24 = 16 x (16+2y).
  
  Manipulating, 16 + 2y = 24 x 24 / 16 = 36
  
  y = 10 cm
  
  Since the radius of the circle = red line + y, radius = 16 +10 = 26cm.
• lpx88

  10 Jun 07, 11:39

  Cud de ans be 22 also?
• DrAlienology

  10 Jun 07, 12:34

  i got like, 27.313.
  
  doubt the anws is 24, since the radius of the circle cannot be the same as the length of the blue line..
• hegu

  10 Jun 07, 13:06

  i got 26 cm