Questions tagged [triangle]
A geometry puzzle centered around the triangle or the centers of a triangle.
37 questions
0
votes
0
answers
74
views
Acute Triangles with a Table Saw [duplicate]
It is your twin 9 year old children’s birthday today. They love triangles and you love your new table saw. You cut a 4x8 sheet of ply corner to corner and present each of them with their present. Your ...
- 11
7
votes
4
answers
2k
views
An impossible(?) triangle
Does a triangle with three right angles exist? Sure, on a sphere you just draw it around an octant. But can you make one on a flat sheet of paper?
The paper can be cut, folded or wrapped in any way ...
- 2,714
12
votes
1
answer
399
views
Specific triangle sides in a grid
Fill each cell with an integer from 1-7 so each number appears exactly once in each
row and column. In each group of three cells, the three numbers must be valid lengths for
the sides of a non-...
4
votes
5
answers
2k
views
Professor Rackbrane: Count the triangles
Professor Rackbrane has just given me the following puzzle as an example of those that interested his party at Christmas. Draw a pentagon, and connect each point with every other point by straight ...
2
votes
0
answers
166
views
Multiple Line Lengths around 8 triangles
The image below contains 8 triangles each having side length 6.
Inside each triangles are three numbers indicating lengths of 3 lines that are wrapped around the triangle without gaps.
Numbers range ...
- 621
5
votes
1
answer
307
views
Circle inscribed in triangle problem [closed]
You need to find the angle BEC knowing that the side BC is tangent to the circumference.
- 71
9
votes
2
answers
681
views
Triangles to diamonds
Given a triangle ABC with sides a=|BC|,b=|CA|,c=|AB| a diamond is circumscribed around the triangle's incircle. The diamond and the triangle share the corner C along with (part of) sides a and b.
...
- 14.5k
12
votes
2
answers
1k
views
Prove why this mechanical linkage for a triangle centroid works
I saw on Twitter this cool mechanical linkage for which the red dot corresponds to the centroid of the triangle defined by the blue dots:
Can you prove why this linkage works?
- 338
-4
votes
1
answer
144
views
Can you help to solve this triangle puzzle [closed]
Find the missing number (triangle)
Please write the logic also.
- 95
4
votes
2
answers
821
views
A geometric puzzle. What is the angle?
This is a simply stated geometry puzzle. What is the angle p in this isosceles triangle?
Here's some information about the origin of the puzzle. Following any links therein may spoil the fun if you ...
- 8,542
-1
votes
2
answers
171
views
Surrounding an equilateral triangle
You are given an equilateral triangle. What is the most number of such identical triangles you can place such that they do not overlap, but each one touches the original triangle?
- 39.7k
8
votes
3
answers
505
views
A circle touches two sides of a triangle and two of its medians
A circle touches two sides of a triangle and two of its medians. Prove that the triangle is isosceles.
This problem came from the Mathematical Digest issue 62 (Jan 1986) which in turn cited a Russian ...
- 24.3k
3
votes
2
answers
256
views
A triangle inside a triangle
All sides of a triangle T1 are shorter than the shortest side of a triangle T2.
Is it always possible to put triangle T1 completely inside triangle T2?
- 13.2k
5
votes
1
answer
224
views
Find the least expense?
You want to build a shop between three roads in the shape of an equilateral triangle.
What would be the best location for the shop so that you can reach each road with the minimum transportation ...
- 1,044
-4
votes
1
answer
174
views
How many cubes is this tringle made of? [closed]
can you guess?
i know its a simple puzzle but lest just have fun
- 455
9
votes
2
answers
1k
views
3D? No-no! 3 Sides
Introducing the Isometric Nonogram!
α) "Boar"ing Definition [oink]
Column: Blue Part + Green Cell
Row: Yellow Part + Green Cell
Adjacent/ Continuous cells: Purple Cell + any of the Orange ...
- 21.7k
7
votes
1
answer
369
views
What percentage of blue? [closed]
Lines are drawn parallel to the base of the triangle, dividing the other sides into 10 equal parts.
Every second strip is painted blue.
Question
What is the percentage of blue color in the ...
user60999
27
votes
4
answers
4k
views
What is the most triangles you can make from a capital "H" and 3 straight lines?
So start with an upper case H, and then draw $3$ straight lines. What is the greatest number of closed triangles that you can form? For example:
Note that triangles inside of triangles only count once ...
- 383
9
votes
3
answers
562
views
Special triangles in convex polygons
Given identical 30-60-90 triangles, what is the convex polygon with the highest number of sides that I can build from them?
This seems a very easy task by first look, but I’m totally stuck right now. ...
1
vote
1
answer
115
views
Can you help me out with this question? [closed]
I found that 3abc+a+b+c formula is correct first and second triangle.
But the result for third triangle isn't in the options.
Can you find another solution?
Source: It's from an old job admission ...
- 111
5
votes
2
answers
606
views
20 right isosceles triangles into a square
Similar:
Unlucky tiling: Arrange thirteen right isosceles triangles into a square
Five graded difficulty isosceles right triangle into square tilings
Two difficult "Seventeen right isosceles ...
- 4,505
3
votes
2
answers
270
views
Two difficult "Seventeen right isosceles triangles into a square" tilings
Similar to:
Unlucky tiling: Arrange thirteen right isosceles triangles into a square
Five graded difficulty isosceles right triangle into square tilings
V.hard problem, 20 right isosceles triangles ...
- 4,505
5
votes
2
answers
342
views
Five graded difficulty isosceles right triangle into square tilings
Similar to:
Unlucky tiling: Arrange thirteen right isosceles triangles into a square
Two difficult "Seventeen right isosceles triangles into a square" tilings
V.hard problem, 20 right ...
- 4,505
11
votes
2
answers
818
views
Unlucky tiling: Arrange thirteen right isosceles triangles into a square
Link to next puzzle in this series:Five graded difficulty isosceles right triangle into square tilings
Two difficult "Seventeen right isosceles triangles into a square" tilings
V.hard ...
- 4,505
4
votes
0
answers
236
views
2018 January Challenge: Geometry [closed]
Considering it's the beginning of a new year, I have created the following challenge. I hope to make one every month until December 2018!
Here goes:
Show that $AD-AB>AC^3$. Do not use scale ...
- 3,674
6
votes
2
answers
419
views
Independent Triangles with Straight Lines
Your task is to create independent triangles (which means they do not have the same edge) by drawing straight lines as exemplified below:
In this example, there are $5$ lines and $5$ independent ...
- 33.8k
0
votes
1
answer
498
views
Triangle partial length of hypotenuse [closed]
How can I solve for X?
What I did was solve for C, and then took (6/6+2)*C. It seems to work but I am not completely sure. Is there a better way?
- 13
2
votes
1
answer
242
views
How to map barycentric indices to a single integer? [closed]
how can one map barycentric indices to a single integer?
e.g.
Edit: added correct image
- 201
34
votes
5
answers
2k
views
Slicing a rectangle
A friend presented this nice little puzzle to me yesterday. You're given a rectangle which is dissected by one of its diagonals, as well as another line that only meets one of the two remaining ...
- 1,621
-1
votes
1
answer
246
views
Trianglify the Shapes
For each of the following shapes, draw extra lines to divide the shape into the smallest number of triangles that can completely fill the shape.
Example:
Solution:
Shapes (a correct answer answers ...
- 297
7
votes
3
answers
2k
views
Can you make 10 triangles with just 10 sticks?
Can you make 10 triangles with just 10 sticks?
The sticks don't have to have the same length.
Hint 1:
There are several other possibilities than the one I gave hints for.
I recently found one with ...
- 4,133
3
votes
6
answers
2k
views
Find the total number of triangles in the diagram
The title of the question says everything $\ldots$
My attempt:
We count $2(1+1+1+2+1+1+2+1+1+1+1)=26$ triangles. (On each side $13$ triangles, and then multiplied by $2$). And then we combine them ...
- 474
-2
votes
2
answers
694
views
That's a lot of triangles
Counting the triangles in this image individually would take far too long. What is a human (not computer) algorithm to figure out how many triangles are in this shape? Answers should include the ...
- 147
1
vote
1
answer
991
views
Four similar triangles
The challenge as described hereafter is to create a total of 4 similar triangles by drawing 4 triangle in a scalene, acute triangle - out of the 5 resulting triangles (4 that make the original one)
...
- 2,239
22
votes
7
answers
3k
views
Triangle in a circle
Suppose three points are chosen at random in a circle. A triangle is made with these three points as vertices.
What's the probability that the triangle contains the origin of the circle?
(Although I ...
- 371
8
votes
1
answer
366
views
The Erasmus tedrahedron
Professor Erasmus has constructed a special tetrahedron that he modestly calls the "Professor-Erasmus-tetrahedron". The professor claims that all four faces of his tedrahedron are right-angled and ...
- 46.4k
10
votes
3
answers
939
views
The Erasmus isosceles triangle
Professor Erasmus has constructed a special isosceles triangle that he modestly calls the "Professor-Erasmus-triangle". The professor claims that he can cut his triangle into three smaller triangles, ...
- 46.4k