Olympiad question: What's the diameter?

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  • Опубліковано 15 жов 2024
  • What's the diameter? This is taken from Philippines Maths Olympiad 2020.
    #maths
    #mathematics
    #math
    #mathpuzzles #geometry

КОМЕНТАРІ • 15

  • @KipIngram
    @KipIngram 27 днів тому

    Well, by quick inspection we have the following equations:
    r*sin(A1) = 7.5
    r*sin(A2) = 3.5
    4*A1 + 2*A2 = 180
    So right away we have three equations in three unknowns. Manipulate the third equation:
    4*A1 + 2*A2 = 180
    2*A1 + A2 = 90
    A2 = 90 - 2*A1
    Substitute into the first to equations:
    r*sin(A1) = 7.5
    r*sin(90-2*A1) = 3.5 --> r*cos(2*A1) = 3.5 --> r*(1-2*sin^2(A1)) = 3.5
    Now let u = sin(A1). Then
    r*u = 7.5 --> u = 7.5/r
    r*(1-2*u^2) = 3.5 --> r*(1-2*(7.5/r)^2) = 3.5
    r - 2*7.5^2/r = 3.5
    r^2 - 3.5*r - 2*7.5^2 = 0
    Roots are 12.5 and -9. A negative radius won't do, so r=12.5, d = 25.
    Q.E.D.

  • @zdrastvutye
    @zdrastvutye 7 місяців тому

    the following algorithm works, unless l10 then xs11=xs1 else xs12=xs1
    90 if abs(dg)>1E-10 then 80
    100 print "der radius=";r:mass=1E3/2/r:goto 120
    110 xbu=x*mass:ybu=y*mass:return
    120 x=r*2:y=0:gosub 110:xba=xbu:yba=ybu:for a=1 to nu:wa=a/nu*pi
    130 x=r*cos(wa):x=x+r:y=r*sin(wa):gosub 110:xbn=xbu:ybn=ybu:goto 150
    140 line xba,yba,xbn,ybn:xba=xbn:yba=ybn:return
    150 gosub 140:next a:x=0:y=0:gosub 110:gcol4:xba=xbu:yba=ybu:x=xs1:y=ys1:gosub 110
    160 xbn=xbu:ybn=ybu:gosub 140:x=xs2:y=ys2:gosub 110:gcol5:xbn=xbu:ybn=ybu:gosub 140
    170 x=2*r:y=0:gosub 110:xbn=xbu:ybn=ybu:gcol6:gosub 140
    der radius=12.5
    >
    run in bbc basic sdl and hit ctrl tab to copy from the results window

  • @hanswust6972
    @hanswust6972 11 місяців тому +4

    I did enjoy the video, your straightforward style is awesome; I suscribe right now.

  • @Ivan-Matematyk
    @Ivan-Matematyk 11 місяців тому +2

    Let AB=d, BC=CD=15, DA=7, E be the point of intersection of the lines AD and BC. Since DC=BC and AD are the diameter, AC is the bisector and height of the BAE triangle. Therefore, AE=AB=d, BC=CE=15.
    From the equality EA * ED = EB * EC we get the equation d*(d-7) = 30 * 15. It follows that d=25. The root d=-18 does not satisfy.

    • @s.s2938
      @s.s2938 4 місяці тому

      Well done dude, only mistake AB is diameter instead of AD

  • @DanMusceac
    @DanMusceac 11 місяців тому

    A more simple way:put the 7cord between the two 15 cords ; now the spalier chord îs paralel with the diameter.From the center of the circle draw a line perpendicular on the smaler chord. Draw another line between the center of the circle and the point between the small and large chord. Now apply the Pitagorian teorema în the two triangles!

    • @MindMathEnigmas
      @MindMathEnigmas  11 місяців тому

      This is clever, turning a non-symmetric problem to a symmetric one.

  • @sarvajagannadhareddy1238
    @sarvajagannadhareddy1238 6 місяців тому

    HOW TO FIND THE EXACT EXACT EXACT CIRCUMFERENCE OF CIRCLE
    . Procedure
    Step 1. Draw a square, 2 diagonals and inscribe a circle in the square. Thereby side and diameter will be the same Step 2 : Subtract 2 diagonals from the perimeter of square Step3. Divide step2 with 8 Step4. Add 3 times of the side. to Step 3
    At the end we get the EXACT circumference of the inscribed circle

  • @howardaltman7212
    @howardaltman7212 11 місяців тому +1

    I did it with trig; your way is much better. Nice!

  • @RameshBas2014
    @RameshBas2014 9 місяців тому +1

    beautiful!

    • @PSYCH_IITR
      @PSYCH_IITR 8 місяців тому +1

      I'm 𝗰𝗵𝗮𝗹𝗹𝗲𝗻𝗴𝗶𝗻𝗴 you to solve this 𝗺𝗮𝘁𝗵 𝗽𝗿𝗼𝗯𝗹𝗲𝗺 and if you will be able to solve this i'll give you money as a reward. 𝗩𝗶𝗱𝗲𝗼 𝗹𝗶𝗻𝗸-:ua-cam.com/video/iFN4DMh8Wto/v-deo.htmlfeature=shared

  • @ChannelTerminatedbyYouTube
    @ChannelTerminatedbyYouTube 6 місяців тому

    Would you rather vibes 💀💀💀

  • @Mecha_Math
    @Mecha_Math 5 місяців тому

    Very good teacher

  • @saumyaadhikari8078
    @saumyaadhikari8078 10 місяців тому +1

    25

  • @Hayet-jb2sd
    @Hayet-jb2sd 11 місяців тому +1

    Oui tres beau