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Two Polygons (Posted on 2008-10-29) Difficulty: 3 of 5
There are two regular polygons: one with X sides and one with Y sides with Y>X. Also, coincidentally, the latter has internal angles that are each (Y-X) degrees greater than the former. Also, X+Y is a perfect square.

What are X and Y?

  Submitted by Charlie    
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Solution: (Hide)
X and Y are 9 and 40 respectively.

DEFDBL A-Z
FOR n1 = 3 TO 100
sr = INT(SQR(n1 + 1))
DO
 sum = sr * sr
 n2 = sum - n1

 IF n2 > 0 THEN
   a1 = 180 - (360 / n1)
   a2 = 180 - (360 / n2)
   IF a2 - a1 = n2 - n1 THEN PRINT n1; n2, a1; a2
 END IF
 sr = sr + 1
LOOP UNTIL sr > 1000
NEXT

The program checks that X+Y is a perfect square and that the difference, in degrees, in the internal angle equals the difference of the number of sides.

The output:

8  8          135  135
9  40         140  171
18  18        160  160
32  32        168.75  168.75
40  9         171  140
50  50        172.8  172.8
72  72        175  175
98  98        176.3265306122449  176.3265306122449

shows only one instance where Y>X-- that is, X=9 and Y=40.


From Enigma No. 1513, by Richard England, New Scientist, 27 September 2008.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
AnswerK Sengupta2008-12-27 06:16:20
Time of the essenceed bottemiller2008-10-29 20:04:20
Some Thoughtsre: solutionPaul2008-10-29 15:36:43
SolutionsolutionDej Mar2008-10-29 11:11:25
Half past Nine in the AM and then someed bottemiller2008-10-29 11:10:49
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