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Questions tagged [geometry]

For questions related to geometric shapes, congruences, similarities, transformations, as well as the properties of classes of figures, points, lines, angles.

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Math textbook for secondary school using Logo like language

What math textbooks for kids do you know that use Logo or similar languages with visual robots like Turtle (in "The Turtle Geometry") that demonstrate space motions, transformations of all ...
paus's user avatar
  • 83
1 vote
1 answer
96 views

Math textbook for secondary school using Logo like syntax

What math textbooks for kids do you know that use Logo or similar languages with visual robots like Turtle (in "The Turtle Geometry") that demonstrate space motions, transformations of all ...
paus's user avatar
  • 83
4 votes
0 answers
130 views

When can students understand the intersection of two circles?

I'm interested in learning two transitions: (1) When can students reason (intuitively, but accurately) to conclude that two circles in the plane could intersect in $0$, $1$, or $2$ points, or are ...
Joseph O'Rourke's user avatar
2 votes
2 answers
170 views

Comparison of two ways to introduce translation to 12-14 year olds

I consider pupils 12-14 years old, who are new to translation. On the other hand, they have been accustomed to placing points in a coordinate system, especially when studying relative numbers. In ...
Stéphane Jaouen's user avatar
2 votes
1 answer
221 views

About a difficult exercise for 12 years pupils

You have to go from a point $A$ (start) to a point $B$ (arrival) by crossing a river $(d)$ and traveling as little distance as possible. Pupils first do a search by trying several paths $1,2,3,4$ and ...
Stéphane Jaouen's user avatar
4 votes
2 answers
178 views

Infinite descent method in geometry

What are the examples we can use to explain infinite descent as an efficient method of proofs in geometry? I think one of the best may be proving medians of a triangle are concurrent by the infinite ...
Janaka Rodrigo's user avatar
11 votes
5 answers
2k views

Textbook For a Course on Classical Geometry

I have been assigned to teach a first year course in geometry the next academic year. This course has been running for quite a while in the university, but of late, has been thought of as redundant ...
Aravind Gundakaram's user avatar
1 vote
1 answer
177 views

Proof that volume of cone is 1/3 that of a cylinder [closed]

I am trying to verfy the formula for "cone volume" calculation. It is not clear why cone volume is 1/3 of a cylinder volume with the same bottom size and height. Is there any proof of the ...
kampmannpeine's user avatar
8 votes
3 answers
4k views

What are some common errors and misconceptions about the Pythagorean Theorem?

I'm teaching a geometry class and want to ensure my students understand the most common errors and misconceptions related to the Pythagorean Theorem and its applications. I attempted an initial Google ...
Humberto José Bortolossi's user avatar
1 vote
2 answers
300 views

Is there a particular reason why segment addition postulate and partition postulate are two different things?

I could be wrong but those two ideas sound the same, just that the partition postulate is more general. There is also the angle addition postulate. The segment addition postulate states that if three ...
Lenny's user avatar
  • 1,068
2 votes
5 answers
985 views

Geometrical verifications for Algebraic formulae

What is the importance of using approaches related to Geometric Algebra in teaching,is it only useful when introducing Algebra to the students or can it be helpful to improve creative skills in ...
Janaka Rodrigo's user avatar
6 votes
5 answers
6k views

What benefit is there to obfuscate the geometry with algebra?

Consider: In a right triangle: sin(2x + 4) = cos (46) What is the value of x? The question above is from standardized tests for a geometry course. If my goal is to have students understand ...
Lenny's user avatar
  • 1,068
1 vote
3 answers
304 views

Is it correct to state that a cone has no faces?

Faces are attributes of polyhedra, so it doesn't make sense to ask how many faces a cone has. Are there traditional scholars that use faces attached to cones? How do different countries deal with the ...
Humberto José Bortolossi's user avatar
7 votes
5 answers
3k views

How to properly define volume for beginner calculus students?

I'm interested in opinions based on experience about how to introduce volume for beginner calculus students. Below I present some observations and specific questions. In Stewart's book, the volume of ...
Pedro's user avatar
  • 1,800
2 votes
2 answers
343 views

Geometric line: constructing fractions

I am interested in teaching maths visually. in page 36 of Growing ideas of number (by John N Crossley) the following image appears, yet I cannot fully grasp how to interpreted it.
GJC's user avatar
  • 147
4 votes
7 answers
328 views

How to convince a student without calculus that great circles are geodesics in a sphere?

how to convince or demonstrate to a high school student who does not know differential and integral calculus that the geodesics of a sphere are arcs of great circles?
Humberto José Bortolossi's user avatar
0 votes
2 answers
387 views

How to explain square meters?

How can we explain to students these ideas? A square with 4 sides measuring 25 cm each does not have an area of 1 square meter. A shape which is not a square can have an area of 1 square meter. Is “...
learningBitByBit's user avatar
8 votes
5 answers
2k views

Models for spherical geometry

Context: I am an associate professor at a small liberal arts institution in the US. I am currently preparing to teach geometry this fall. Our course is mostly focused on Euclidean geometry (it's ...
AegisCruiser's user avatar
  • 1,427
1 vote
1 answer
626 views

Triples or triplets in Pythagoras theorem

We usually say (3,4,5) , (5,12,13) as Pythagorean triples. What is much better way to refer those sets of numbers, Pythagorean triples or Pythagorean triplets? According to the normal usage we say ...
Janaka Rodrigo's user avatar
0 votes
2 answers
161 views

Multiple proofs for the same problem

One way of encouraging students to explore mathematics can be letting them to use different approaches to solve the same problem. If students can find alternatives from different areas of mathematics ...
Janaka Rodrigo's user avatar
2 votes
3 answers
170 views

Geometrical approaches in algebra

Usually we describe proofs in algebra by algebraic means, I think it may be useful to introduce geometrical approaches to those proofs to improve creativity skills of students, what are the examples ...
Janaka Rodrigo's user avatar
3 votes
1 answer
379 views

Best demonstration of $\pi$ ever; is this common?

When I was in 6th grade (U.S. so 12-13 years old), I took a summer school class. The teacher gave us all different sized spools (spools that hold sewing thread but were empty). We each made a mark on ...
Daniel's user avatar
  • 229
0 votes
1 answer
231 views

How to formalize high-school (Euclidean) geometry?

I have unsuccessfully attempted several times over the years to formalize high-school (Euclidean) geometry, or even a working subset of it. Think very simple, diagramless geometry. The usual two-...
Dan Christensen's user avatar
6 votes
3 answers
1k views

Geometry in the Community College Curriculum

As many Americans know, the “traditional” high school sequence is: Algebra 1 Geometry Algebra 2 PreCalculus Calculus For those who take developmental education at the community college level, it ...
MichaelLink's user avatar
11 votes
4 answers
3k views

How can I build a protractor without a protractor?

We all know how to use a protractor; it is taught in elementary school. However, I was wondering what type of knowledge is required to build one from scratch. For instance, was the understanding of $\...
YGranja's user avatar
  • 119
5 votes
2 answers
971 views

Is "Annular Ring" redundant?

I've come across the term annular ring in parentheses following washer in my calculus textbook: "has the shape of a washer (an annular ring)". The definition of the word "annular" ...
Brian's user avatar
  • 153
20 votes
4 answers
6k views

Explaining why volume of cone is a third of cylinder

I came across this video explaining to kids why the volume of a cone is a third of the cylinder of same cross-sectional radius and height. Essentially the explainer presents pre-created cylindrical ...
Bravo's user avatar
  • 303
10 votes
2 answers
790 views

Real-world applications of taxicab metric

The taxicab metric can be used to measure distances in idealized gridded cities. However, usually this serves only as a fun exercise for students. I'm looking for engaging (as non-technical as ...
Paula's user avatar
  • 251
7 votes
1 answer
133 views

Resources for Teaching Parameterization of Curves/Surfaces

In classes like Calc 3 or Computer Graphics, I want my students to be comfortable describing common curves and surfaces parametrically (such as lines, triangles, circles, or surfaces of revolution). ...
TomKern's user avatar
  • 4,425
7 votes
7 answers
515 views

Creative problems in 2D vector geometry

What are some "interesting" and creative problems or exercises on specifically 2-dimensional vector geometry that a high school student might find compelling to solve? The class' current ...
Damian Reding's user avatar
0 votes
1 answer
268 views

Why do so many children's book confuse discs with circles? [duplicate]

The difference between a disc (disk) and a circle is crystal clear to me: However, in many children's books, a disc is usually called a circle: Why do many children's book confuse discs with circles?...
Zuriel's user avatar
  • 4,275
2 votes
2 answers
236 views

Is there a good Animation to explain Rotational Symmetry of Equilateral triangle

I am willing to teach that the Order of rotational Symmetry of Equilateral triangle as $3$ using Animation. Any suggestions of good applet which demonstrates the rotation of equilateral triangle with ...
Ekaveera Gouribhatla's user avatar
4 votes
1 answer
298 views

Valid Reasons in Two-Column Geometry Proofs

I'm wondering about the relationship between Eculid's work and modern high school geometry. In "two column proofs," certain reasons are considered acceptible for steps in the proof, such as ...
Robin Andrews's user avatar
13 votes
3 answers
3k views

How do I sketch a good gaussian curve freehanded, or by using only common sketching tools?

I'm a lousy artist. If I want my Gaussian curves to be accurately drawn when I use a whiteboard, or work with pen & paper, what are my options? Is there a way to use a straight edge, or compass, ...
Kiteration's user avatar
3 votes
2 answers
154 views

Line segments on a geoboard

To make a polygon on a traditional geoboard, one usually stretches a rubber band around the vertices. No problem there. When making a simple line segment, however, a rubber band is typically stretched ...
EJ Mak's user avatar
  • 329
3 votes
2 answers
701 views

Where can I buy a compass that can hold an "Expo" dry erase whiteboard marker?

Question in title. I'd like to draw a perfect circle on the whiteboard using "expo" dry erase markers. Is there a store I could buy such a compass at? Thank you
Ferris Boyler's user avatar
0 votes
1 answer
126 views

Names of two circle theorems in English [closed]

There are two theorems: All three angles AC_1B, AC_2B, AC_3B are equal. In general: All angles above a chord are equal. The size of any angle above a chord AB is half the size of angle AOB where O is ...
Jan's user avatar
  • 9
3 votes
4 answers
357 views

Explain to 10 year old — Why do 3D mental pictures usually suffice for high-dimensional geometry?

My 10 year old daughter is trying to read this book — please explain in Simple English that she'll grasp. Kindly see the embolded phrases below. The author doesn't expound why the 3D "mental ...
user avatar
4 votes
5 answers
477 views

Is it a good idea for elementary school students to observe and discover the "circle perimeter formula" themselves without being dictated to?

Let them discover $\;\ell=2\pi R\;$ by their own, at least the invariance of $\ell/R$ Do you think that the following method works well in a mathematics class of elementary school? What do you think ...
Ali Taghavi's user avatar
24 votes
9 answers
5k views

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

The assumed age of the students is 10-15 years old. What is the danger in saying that two triangles are "the same" or "equal" instead of saying that they are congruent? It seems to ...
Improve's user avatar
  • 1,881
17 votes
12 answers
7k views

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

The imagined students are in elementary school, say around 9-13 years old. I want to use rather precise terminology when talking to my students. However, it seems like we typically use the same ...
Improve's user avatar
  • 1,881
4 votes
2 answers
268 views

Are there any list of mathematical constructions which can challenge 12-16 year old students?

Mathematical (geometric) constructions are an interesting way to engage students. It also helps in better understanding of different geometrical properties. For example, Sierpinski triangle or square, ...
GanitCharcha's user avatar
5 votes
2 answers
303 views

Geometric and Graphical perspective on completing the square

I just read an interesting article that helps to understand completing the square, and prove the quadratic equation from a geomterical perspective. My question is how do I understand the graphical ...
Joseph Gutstadt's user avatar
7 votes
7 answers
4k views

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

I am teaching 12-16 year olds. How should I write down the Pythagorean theorem equation? Some alternatives: $a^2 + b^2 = c^2$ $\text{leg}^2 + \text{leg}^2 = \text{hypotenuse}^2$ $\text{leg}_1^2 + \...
Improve's user avatar
  • 1,881
0 votes
1 answer
206 views

Matriculation exams like in Europe

I just looked at matriculation exams from Finland. They have both basic and advanced level exams. Most US high school seniors could not pass the basic exam. If each US state were to create its own ...
user50896's user avatar
7 votes
8 answers
1k views

What is a good second book in high school geometry?

I have been looking at questions on Math Stack Exchange and I am frequently coming across topics that sound as if they could have been optional chapters in a high school geometry class, but I have ...
RobertTheTutor's user avatar
28 votes
10 answers
3k views

Should figures be presented to scale?

I've been working with a teacher, helping her with tech. One of the things I help with is to convert PDF formatted quizzes or tests to DeltaMath for the students to take online. The issue that I face ...
JTP - Apologise to Monica's user avatar
4 votes
4 answers
305 views

Can we define length and perpendicularity not via an inner product?

A natural way to reason about Euclidean geometry using modern mathematical language is to define Euclidean space as an affine space $A$ directed by a finite-dimensional real vector space $V$. However, ...
harius's user avatar
  • 61
7 votes
2 answers
283 views

Is $\overline{AB} \cong \overline{BA}$ usually taught as an instance of the symmetric property of congruence?

I have been tutoring a wide range of math subjects for many years. Recently, I began tutoring a girl in high school geometry (in California, for context). This semester of the course is starting with ...
Geoffrey's user avatar
  • 898
9 votes
3 answers
2k views

Definition of Trapezoid

From one textbook we use in our High School - Transcription: A trapezoid is a quadrilateral with exactly one pair of parallel sides. The parallel sides are called bases of the trapezoid. And from ...
JTP - Apologise to Monica's user avatar