# Tag Info

### Is this homework problem on counting triangles within a 4x4 grid too vague?

This is a bit of a can of worms. Let's unpack a little. We were given no additional information other than that stated in the page. This is your daughter's homework, not yours. Be careful with ...

### Why do we introduce the notion that triangles are "congruent" instead of just saying that they are "the same" or "equal"?

Colloquially, there's a lot of conceptual overlap between all of these terms, but "sameness" is not a well-defined mathematical property. Congruent shapes need not be "the same" or ...

### Why should kids learn how to use a compass and straightedge, and not rely on a drawing program?

The point of compass-and-straightedge constructions is for the students to get experience reasoning about axiomatic systems. The accuracy of the actual drawings is basically irrelevant (as long as it'...
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### Why we have to be so precise in Geometry?

Because the aim of geometry is to study properties related to shape, size and length. Therefore, in the context of geometry, we cannot deform our objects because deformation changes these properties. ...

### What can (and should) an educator do about ambiguous terms like "triangle", "square", etc?

I'm confused. Are you really going to try to make this sort of distinction when teaching geometric figures to students "around 9-13 years old"? Students that age (and engineers my age -- ...

### In what curricula are "rectangles" defined so as to exclude squares?

I cannot answer the OP's question about cross-cultural/international perspectives, but here is a historical perspective that may be helpful. The issue here (whether the category "rectangles"...
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### Beautiful planar geometry theorems not encountered in high school

Given that I had a good time coercing Mathematica to give me the pictures below I might as well promote my comment to an answer. My favorite such a result is the so called Steiner's porism. It is a ...

### Why do we introduce the notion that triangles are "congruent" instead of just saying that they are "the same" or "equal"?

The smart-aleck answer is that most congruent triangles, or congruent figures more generally, aren't actually "the same" or "equal". Usually when we say two things are "the ...
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### Explaining why volume of cone is a third of cylinder

This is an experiment which can lead you to guess that the volume of a cone is approximately $\frac{1}{3}$ the volume of a cylinder with the same base and height. It is not a proof in any sense of ...

### What can (and should) an educator do about ambiguous terms like "triangle", "square", etc?

One encounters exactly the same issue teaching multivariable calculus when one treats integrals over three-dimensional regions and integrals over the surfaces that are their boundaries. In particular ...

### Given a 3 4 5 triangle, how do you know that it is a right triangle?

The Chinese came up with the following a long time ago. Probably something better, but this is the gist of it. Let's start with a right triangle with height b=4 and base a=3. We know it has some ...

### Given a 3 4 5 triangle, how do you know that it is a right triangle?

Here is a simple construction. Adjust to taste. 1. Draw a line $l$ passing through a point O. 2. Construct circles of radius 3 and 4 with centre O. Call them $C_3$ and $C_4$. Let the intersection of ...

### Given a 3 4 5 triangle, how do you know that it is a right triangle?

The fact that there is a 3-4-5 triangle that is a right triangle is unique to the Euclidean plane. There is no such triangle in the spherical or hyperbolic planes. Since the Pythagorean theorem is ...

### Is there a name for paths that follow gridlines?

Generally, this math falls under the scope of what is commonly called Taxicab Geometry. I would use taxicab path as a noun to describe the specific paths illustrated in the original question; whereas ...
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### Should figures be presented to scale?

As an answer so that I can paste in a picture: I think that the problem with the one on the left is that it is possibly "good enough" that someone might think that it is to scale and that ...

### What can (and should) an educator do about ambiguous terms like "triangle", "square", etc?

I think the distinction you are raising is not natural to students at this age. I teach undergraduates and graduate students, not elementary schoolers, but I find that it is not natural for ...

### Are kindergartners supposed to be steered from squares being rectangles?

Kindergartners are generally at an early stage of geometric development, in which shapes are recognized by how well they resemble prototypical images, rather than by whether or not they conform to a ...
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### How do I sketch a good gaussian curve freehanded, or by using only common sketching tools?

I would put dots where I want 1 standard deviation to be, because I know that's where the inflection points are. (I just graphed $y=e^{-x^{2}/2}$ on desmos, and I see that the inflection points are at ...

### Real-world examples of more "obscure" geometric figures

The hexagon at the north pole of Saturn:   It is known that "[regular shapes] form in an area of turbulent flow between ... two different rotating fluid bodies with dissimilar speeds." and ...

### Why do we care about multiple proofs of the same theorem?

I'd say different proofs usually employ different techniques, which in turn might be applicable to different sets of other theorems. So the more proofs I know for one theorem, the higher the chances ...
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### Co-curricular lessons between geometry and chemistry?

One angle you could look at is molecular geometry. Not really my subject area but a couple of examples: Organic molecules can have different chiralities. That means that while one is the mirror image ...

### Should figures be presented to scale?

There is no value in drawing the figure exactly to scale, but the left-hand figure is inaccurate to the point where it is positively misleading. Since the angle marked 30 degrees is actually drawn ...

### What is the preferred way to denote the Pythagorean theorem equation?

Common knowledge The formula $a^2+b^2 = c^2$ is common knowledge and the words for hypotenuse and leg (is "cathetus" not used in English?) are basic mathematical vocabulary. Including these ...

### Given a 3 4 5 triangle, how do you know that it is a right triangle?

Graph paper (or square floor tiling) to the rescue! Proof by picture for a 3 4 5 triangle: Because the drawing is on the grid and not the skew tiling of the square on the hypotenuse, determining ...

### Why should kids learn how to use a compass and straightedge, and not rely on a drawing program?

Of course there is the deep (~2000 yrs) history of compass/straightedge constructions. Another more modern alternative is origami constructions: Robert Lang, "Origami and Geometric Constructions,"...
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### How to give my students a straightedge instead of a ruler

I have lots of ideas, which, it turns out, aren't going to fit into a comment. If you don't need something too long, but want something that is pretty uniform and consistent, popsicle sticks (also ...