Checkerboard Triangle Again

Geometry Level 4

Which area is larger?

Equal area Yellow area Pink area

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1 solution

Calvin Lin Staff
Sep 23, 2016

[Michael Mendrin pointed out that my answer is wrong. I found the error in my proof. The yellow area is indeed larger, just slightly. I do not yet know of a simple demonstration of this result, other than through tedious calculation.]


Can you generalize this result to a right triangle of sides m m and n n ?

[Note: I am yet unable to generalize the result. I do not know if it will be larger in cases of different parity, but I suspect that is the case.]

@Michael Mendrin Yea, the calculations are a ton worse than I expected.

I've been trying to do a continuity argument from the even-even to the even-odd to the odd-odd case, but that doesn't seem to lead me anywhere.

IE In the 4 by 6, the yellow and pink areas are the same. So let's consider the additional triangle with vertices ( 0 , 4 ) , ( 6 , 0 ) , ( 7 , 0 ) (0,4), (6,0), (7,0) . But, that would cause me to think that the pink area is larger, mainly because of the bottom right triangle.

I suspect it has some number-theoretic relevance / consequence, and might try phrasing it that way.

Calvin Lin Staff - 4 years, 8 months ago

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Actually, it is kind of interesting to see the relationship between given a , b a,b and that fraction that either color differs from exactly half of the "area of the half rectangle". It does seem to suggest some kind of a "number-theoretic" relationship here. Maybe a little later, I can post both the equation that generates that fraction and the results. I've been trying to devise a problem for Brilliant, but I think just about everybody is going to find the problem far too tedious to be of any interest.

I'll have to come back to this later as I'm running out of time. Too much to do.

Michael Mendrin - 4 years, 8 months ago

Calvin, I'm frozen out from trying to fix my comment showing results. I can't get in. The "Edit" button don't work, and I have to be out of here now.

Michael Mendrin - 4 years, 8 months ago

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I've edited the Latex to help it display.

The original Latex looks correct, but it was just too long (approx 2000 rows?) for it to get displayed. I've cut it up into smaller chunks (and also reduced the results that are disaplayed.

Calvin Lin Staff - 4 years, 8 months ago

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@Calvin Lin Wow! Thank you very much! Now, notice [any] relationship between a , b a,b and the fractions. I see some intriguing patterns, but so far nothing trivial.

Michael Mendrin - 4 years, 8 months ago

@Calvin Lin Yeah, maybe that's enough for now for some of us to try to see any patterns. It gets interesting when a a becomes 20 20 or 24 24 .

Michael Mendrin - 4 years, 8 months ago

Given the integer sides of the triangle a , b a,b of opposite parity, the following generates the fraction F ( a , b ) F(a,b) that is the absolute difference between the total area of either color with half of the area of the triangle

So, for example, for a = 4 a=4 , and b = 7 b=7 , the absolute difference is 1 28 \dfrac{1}{28}

Michael Mendrin - 4 years, 8 months ago

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Haha, an interesting variant would be to give that formula where a , b a, b have the same parity, and then ask what that value is. I would love to see how someone comes up with the corresponding interpretation for it in terms of area.

Calvin Lin Staff - 4 years, 8 months ago

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With a little more effort, I probably can modify this formula to work for a , b a,b of the same parity as well.

Michael Mendrin - 4 years, 8 months ago

Results in form of a a , b b , and F ( a , b ) F(a,b)

a b F ( a , b ) 2 3 1 12 2 5 1 20 2 7 1 28 2 9 1 36 2 11 1 44 2 13 1 52 2 15 1 60 2 17 1 68 2 19 1 76 2 21 1 84 2 23 1 92 2 25 1 100 2 27 1 108 2 29 1 116 2 31 1 124 2 33 1 132 2 35 1 140 2 37 1 148 2 39 1 156 2 41 1 164 2 43 1 172 2 45 1 180 2 47 1 188 2 49 1 196 2 51 1 204 2 53 1 212 2 55 1 220 2 57 1 228 2 59 1 236 2 61 1 244 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 2 & 3 & \frac{1}{12} \\ 2 & 5 & \frac{1}{20} \\ 2 & 7 & \frac{1}{28} \\ 2 & 9 & \frac{1}{36} \\ 2 & 11 & \frac{1}{44} \\ 2 & 13 & \frac{1}{52} \\ 2 & 15 & \frac{1}{60} \\ 2 & 17 & \frac{1}{68} \\ 2 & 19 & \frac{1}{76} \\ 2 & 21 & \frac{1}{84} \\ 2 & 23 & \frac{1}{92} \\ 2 & 25 & \frac{1}{100} \\ 2 & 27 & \frac{1}{108} \\ 2 & 29 & \frac{1}{116} \\ 2 & 31 & \frac{1}{124} \\ 2 & 33 & \frac{1}{132} \\ 2 & 35 & \frac{1}{140} \\ 2 & 37 & \frac{1}{148} \\ 2 & 39 & \frac{1}{156} \\ 2 & 41 & \frac{1}{164} \\ 2 & 43 & \frac{1}{172} \\ 2 & 45 & \frac{1}{180} \\ 2 & 47 & \frac{1}{188} \\ 2 & 49 & \frac{1}{196} \\ 2 & 51 & \frac{1}{204} \\ 2 & 53 & \frac{1}{212} \\ 2 & 55 & \frac{1}{220} \\ 2 & 57 & \frac{1}{228} \\ 2 & 59 & \frac{1}{236} \\ 2 & 61 & \frac{1}{244} \\ \end{array} a b F ( a , b ) 4 3 5 12 4 5 1 4 4 7 1 28 4 9 1 36 4 11 5 44 4 13 5 52 4 15 1 60 4 17 1 68 4 19 5 76 4 21 5 84 4 23 1 92 4 25 1 100 4 27 5 108 4 29 5 116 4 31 1 124 4 33 1 132 4 35 1 28 4 37 5 148 4 39 1 156 4 41 1 164 4 43 5 172 4 45 1 36 4 47 1 188 4 49 1 196 4 51 5 204 4 53 5 212 4 55 1 220 4 57 1 228 4 59 5 236 4 61 5 244 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 4 & 3 & \frac{5}{12} \\ 4 & 5 & \frac{1}{4} \\ 4 & 7 & \frac{1}{28} \\ 4 & 9 & \frac{1}{36} \\ 4 & 11 & \frac{5}{44} \\ 4 & 13 & \frac{5}{52} \\ 4 & 15 & \frac{1}{60} \\ 4 & 17 & \frac{1}{68} \\ 4 & 19 & \frac{5}{76} \\ 4 & 21 & \frac{5}{84} \\ 4 & 23 & \frac{1}{92} \\ 4 & 25 & \frac{1}{100} \\ 4 & 27 & \frac{5}{108} \\ 4 & 29 & \frac{5}{116} \\ 4 & 31 & \frac{1}{124} \\ 4 & 33 & \frac{1}{132} \\ 4 & 35 & \frac{1}{28} \\ 4 & 37 & \frac{5}{148} \\ 4 & 39 & \frac{1}{156} \\ 4 & 41 & \frac{1}{164} \\ 4 & 43 & \frac{5}{172} \\ 4 & 45 & \frac{1}{36} \\ 4 & 47 & \frac{1}{188} \\ 4 & 49 & \frac{1}{196} \\ 4 & 51 & \frac{5}{204} \\ 4 & 53 & \frac{5}{212} \\ 4 & 55 & \frac{1}{220} \\ 4 & 57 & \frac{1}{228} \\ 4 & 59 & \frac{5}{236} \\ 4 & 61 & \frac{5}{244} \\ \end{array} a b F ( a , b ) 6 3 1 4 6 5 7 12 6 7 5 12 6 9 1 12 6 11 1 44 6 13 1 52 6 15 1 20 6 17 35 204 6 19 35 228 6 21 1 28 6 23 1 92 6 25 1 100 6 27 1 36 6 29 35 348 6 31 35 372 6 33 1 44 6 35 1 140 6 37 1 148 6 39 1 52 6 41 35 492 6 43 35 516 6 45 1 60 6 47 1 188 6 49 1 196 6 51 1 68 6 53 35 636 6 55 7 132 6 57 1 76 6 59 1 236 6 61 1 244 \begin{array}{ccc|} a & b & F(a,b)| \\ \hline 6 & 3 & \frac{1}{4} \\ 6 & 5 & \frac{7}{12} \\ 6 & 7 & \frac{5}{12} \\ 6 & 9 & \frac{1}{12} \\ 6 & 11 & \frac{1}{44} \\ 6 & 13 & \frac{1}{52} \\ 6 & 15 & \frac{1}{20} \\ 6 & 17 & \frac{35}{204} \\ 6 & 19 & \frac{35}{228} \\ 6 & 21 & \frac{1}{28} \\ 6 & 23 & \frac{1}{92} \\ 6 & 25 & \frac{1}{100} \\ 6 & 27 & \frac{1}{36} \\ 6 & 29 & \frac{35}{348} \\ 6 & 31 & \frac{35}{372} \\ 6 & 33 & \frac{1}{44} \\ 6 & 35 & \frac{1}{140} \\ 6 & 37 & \frac{1}{148} \\ 6 & 39 & \frac{1}{52} \\ 6 & 41 & \frac{35}{492} \\ 6 & 43 & \frac{35}{516} \\ 6 & 45 & \frac{1}{60} \\ 6 & 47 & \frac{1}{188} \\ 6 & 49 & \frac{1}{196} \\ 6 & 51 & \frac{1}{68} \\ 6 & 53 & \frac{35}{636} \\ 6 & 55 & \frac{7}{132} \\ 6 & 57 & \frac{1}{76} \\ 6 & 59 & \frac{1}{236} \\ 6 & 61 & \frac{1}{244} \\ \end{array} a b F ( a , b ) 8 3 1 6 8 5 3 10 8 7 3 4 8 9 7 12 8 11 3 22 8 13 1 26 8 15 1 60 8 17 1 68 8 19 1 38 8 21 1 14 8 23 21 92 8 25 21 100 8 27 1 18 8 29 1 58 8 31 1 124 8 33 1 132 8 35 1 70 8 37 3 74 8 39 7 52 8 41 21 164 8 43 3 86 8 45 1 90 8 47 1 188 8 49 1 196 8 51 1 102 8 53 3 106 8 55 21 220 8 57 7 76 8 59 3 118 8 61 1 122 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 8 & 3 & \frac{1}{6} \\ 8 & 5 & \frac{3}{10} \\ 8 & 7 & \frac{3}{4} \\ 8 & 9 & \frac{7}{12} \\ 8 & 11 & \frac{3}{22} \\ 8 & 13 & \frac{1}{26} \\ 8 & 15 & \frac{1}{60} \\ 8 & 17 & \frac{1}{68} \\ 8 & 19 & \frac{1}{38} \\ 8 & 21 & \frac{1}{14} \\ 8 & 23 & \frac{21}{92} \\ 8 & 25 & \frac{21}{100} \\ 8 & 27 & \frac{1}{18} \\ 8 & 29 & \frac{1}{58} \\ 8 & 31 & \frac{1}{124} \\ 8 & 33 & \frac{1}{132} \\ 8 & 35 & \frac{1}{70} \\ 8 & 37 & \frac{3}{74} \\ 8 & 39 & \frac{7}{52} \\ 8 & 41 & \frac{21}{164} \\ 8 & 43 & \frac{3}{86} \\ 8 & 45 & \frac{1}{90} \\ 8 & 47 & \frac{1}{188} \\ 8 & 49 & \frac{1}{196} \\ 8 & 51 & \frac{1}{102} \\ 8 & 53 & \frac{3}{106} \\ 8 & 55 & \frac{21}{220} \\ 8 & 57 & \frac{7}{76} \\ 8 & 59 & \frac{3}{118} \\ 8 & 61 & \frac{1}{122} \\ \end{array} a b F ( a , b ) 10 3 19 60 10 5 1 4 10 7 51 140 10 9 11 12 10 11 3 4 10 13 51 260 10 15 1 12 10 17 19 340 10 19 1 76 10 21 1 84 10 23 19 460 10 25 1 20 10 27 17 180 10 29 33 116 10 31 33 124 10 33 17 220 10 35 1 28 10 37 19 740 10 39 1 156 10 41 1 164 10 43 19 860 10 45 1 36 10 47 51 940 10 49 33 196 10 51 11 68 10 53 51 1060 10 55 1 44 10 57 1 60 10 59 1 236 10 61 1 244 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 10 & 3 & \frac{19}{60} \\ 10 & 5 & \frac{1}{4} \\ 10 & 7 & \frac{51}{140} \\ 10 & 9 & \frac{11}{12} \\ 10 & 11 & \frac{3}{4} \\ 10 & 13 & \frac{51}{260} \\ 10 & 15 & \frac{1}{12} \\ 10 & 17 & \frac{19}{340} \\ 10 & 19 & \frac{1}{76} \\ 10 & 21 & \frac{1}{84} \\ 10 & 23 & \frac{19}{460} \\ 10 & 25 & \frac{1}{20} \\ 10 & 27 & \frac{17}{180} \\ 10 & 29 & \frac{33}{116} \\ 10 & 31 & \frac{33}{124} \\ 10 & 33 & \frac{17}{220} \\ 10 & 35 & \frac{1}{28} \\ 10 & 37 & \frac{19}{740} \\ 10 & 39 & \frac{1}{156} \\ 10 & 41 & \frac{1}{164} \\ 10 & 43 & \frac{19}{860} \\ 10 & 45 & \frac{1}{36} \\ 10 & 47 & \frac{51}{940} \\ 10 & 49 & \frac{33}{196} \\ 10 & 51 & \frac{11}{68} \\ 10 & 53 & \frac{51}{1060} \\ 10 & 55 & \frac{1}{44} \\ 10 & 57 & \frac{1}{60} \\ 10 & 59 & \frac{1}{236} \\ 10 & 61 & \frac{1}{244} \\ \end{array} a b F ( a , b ) 12 3 1 4 12 5 13 60 12 7 25 84 12 9 5 12 12 11 13 12 12 13 11 12 12 15 1 4 12 17 25 204 12 19 13 228 12 21 1 28 12 23 1 92 12 25 1 100 12 27 1 36 12 29 13 348 12 31 25 372 12 33 5 44 12 35 143 420 12 37 143 444 12 39 5 52 12 41 25 492 12 43 13 516 12 45 1 60 12 47 1 188 12 49 1 196 12 51 1 68 12 53 13 636 12 55 5 132 12 57 5 76 12 59 143 708 12 61 143 732 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 12 & 3 & \frac{1}{4} \\ 12 & 5 & \frac{13}{60} \\ 12 & 7 & \frac{25}{84} \\ 12 & 9 & \frac{5}{12} \\ 12 & 11 & \frac{13}{12} \\ 12 & 13 & \frac{11}{12} \\ 12 & 15 & \frac{1}{4} \\ 12 & 17 & \frac{25}{204} \\ 12 & 19 & \frac{13}{228} \\ 12 & 21 & \frac{1}{28} \\ 12 & 23 & \frac{1}{92} \\ 12 & 25 & \frac{1}{100} \\ 12 & 27 & \frac{1}{36} \\ 12 & 29 & \frac{13}{348} \\ 12 & 31 & \frac{25}{372} \\ 12 & 33 & \frac{5}{44} \\ 12 & 35 & \frac{143}{420} \\ 12 & 37 & \frac{143}{444} \\ 12 & 39 & \frac{5}{52} \\ 12 & 41 & \frac{25}{492} \\ 12 & 43 & \frac{13}{516} \\ 12 & 45 & \frac{1}{60} \\ 12 & 47 & \frac{1}{188} \\ 12 & 49 & \frac{1}{196} \\ 12 & 51 & \frac{1}{68} \\ 12 & 53 & \frac{13}{636} \\ 12 & 55 & \frac{5}{132} \\ 12 & 57 & \frac{5}{76} \\ 12 & 59 & \frac{143}{708} \\ 12 & 61 & \frac{143}{732} \\ \end{array} a b F ( a , b ) 14 3 17 84 14 5 3 28 14 7 1 4 14 9 79 252 14 11 145 308 14 13 5 4 14 15 13 12 14 17 145 476 14 19 79 532 14 21 1 12 14 23 15 644 14 25 17 700 14 27 1 108 14 29 1 116 14 31 17 868 14 33 5 308 14 35 1 20 14 37 79 1036 14 39 145 1092 14 41 65 164 14 43 65 172 14 45 29 252 14 47 79 1316 14 49 1 28 14 51 5 476 14 53 17 1484 14 55 1 220 14 57 1 228 14 59 17 1652 14 61 15 1708 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 14 & 3 & \frac{17}{84} \\ 14 & 5 & \frac{3}{28} \\ 14 & 7 & \frac{1}{4} \\ 14 & 9 & \frac{79}{252} \\ 14 & 11 & \frac{145}{308} \\ 14 & 13 & \frac{5}{4} \\ 14 & 15 & \frac{13}{12} \\ 14 & 17 & \frac{145}{476} \\ 14 & 19 & \frac{79}{532} \\ 14 & 21 & \frac{1}{12} \\ 14 & 23 & \frac{15}{644} \\ 14 & 25 & \frac{17}{700} \\ 14 & 27 & \frac{1}{108} \\ 14 & 29 & \frac{1}{116} \\ 14 & 31 & \frac{17}{868} \\ 14 & 33 & \frac{5}{308} \\ 14 & 35 & \frac{1}{20} \\ 14 & 37 & \frac{79}{1036} \\ 14 & 39 & \frac{145}{1092} \\ 14 & 41 & \frac{65}{164} \\ 14 & 43 & \frac{65}{172} \\ 14 & 45 & \frac{29}{252} \\ 14 & 47 & \frac{79}{1316} \\ 14 & 49 & \frac{1}{28} \\ 14 & 51 & \frac{5}{476} \\ 14 & 53 & \frac{17}{1484} \\ 14 & 55 & \frac{1}{220} \\ 14 & 57 & \frac{1}{228} \\ 14 & 59 & \frac{17}{1652} \\ 14 & 61 & \frac{15}{1708} \\ \end{array} a b F ( a , b ) 16 3 7 24 16 5 3 8 16 7 3 14 16 9 5 18 16 11 31 88 16 13 55 104 16 15 17 12 16 17 5 4 16 19 55 152 16 21 31 168 16 23 5 46 16 25 3 50 16 27 5 72 16 29 7 232 16 31 1 124 16 33 1 132 16 35 1 40 16 37 15 296 16 39 1 26 16 41 5 82 16 43 31 344 16 45 11 72 16 47 85 188 16 49 85 196 16 51 55 408 16 53 31 424 16 55 1 22 16 57 1 38 16 59 15 472 16 61 7 488 \begin{array}{ccc|} a & b & F(a,b) \\ \hline 16 & 3 & \frac{7}{24} \\ 16 & 5 & \frac{3}{8} \\ 16 & 7 & \frac{3}{14} \\ 16 & 9 & \frac{5}{18} \\ 16 & 11 & \frac{31}{88} \\ 16 & 13 & \frac{55}{104} \\ 16 & 15 & \frac{17}{12} \\ 16 & 17 & \frac{5}{4} \\ 16 & 19 & \frac{55}{152} \\ 16 & 21 & \frac{31}{168} \\ 16 & 23 & \frac{5}{46} \\ 16 & 25 & \frac{3}{50} \\ 16 & 27 & \frac{5}{72} \\ 16 & 29 & \frac{7}{232} \\ 16 & 31 & \frac{1}{124} \\ 16 & 33 & \frac{1}{132} \\ 16 & 35 & \frac{1}{40} \\ 16 & 37 & \frac{15}{296} \\ 16 & 39 & \frac{1}{26} \\ 16 & 41 & \frac{5}{82} \\ 16 & 43 & \frac{31}{344} \\ 16 & 45 & \frac{11}{72} \\ 16 & 47 & \frac{85}{188} \\ 16 & 49 & \frac{85}{196} \\ 16 & 51 & \frac{55}{408} \\ 16 & 53 & \frac{31}{424} \\ 16 & 55 & \frac{1}{22} \\ 16 & 57 & \frac{1}{38} \\ 16 & 59 & \frac{15}{472} \\ 16 & 61 & \frac{7}{488} \\ \end{array}

Michael Mendrin - 4 years, 8 months ago

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