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## Simion Filip – Geometry and Physics: from Euclid to Einstein

This Saturday, November 8th, Simion Filip will present the way our understanding of the physical world shaped the geometric problems that we considered throughout history.  Examples will be drawn mostly from elementary Euclidian geometry and the talk should be accessible to anyone who is familiar with angles and triangles.

Mr. Filip is a senior at Princeton University, studying mathematics with an interest in mathematical physics. After graduation, he plans to pursue a Ph. D. in mathematics.  While in high-school, Simion Filip took part in both the International Mathematics and Informatics Olympiads, where he received silver and bronze medals respectively.

## Chengde Feng – Angles and Areas – Recap

Chengde Feng’s lecture was greeted with very high attendance and very active participation.  Throughout his lecture, Mr. Feng showed the students how to solve a wide variety of geometry problems involving area.  These are problems that frequently occur in contests like MATHCOUNTS or AMC.  Many shortcuts and techniques were shared to help shave off precious sections during these problem solving tests.

You knew you were at a Math Circle when in the second hour, Mr. Feng announced a “pop quiz” and instead of groans there was honest enthusiasm from the students eager to apply their new knowledge.

Mr. Feng has provided the problems from the lecture. Members of the Metroplex Math Circle e-mail group can download these files from the group site. To join the e-mail group simply click below.

Click to join MetroplexMathCircle

## Chengde Feng – Angles and Areas – November 1

Chengde Feng, an instructor at AwesomeMath, father of Zuming Feng and a good friend of the Metroplex Math Circle will come to Dallas this Saturday to lecture on “Angles and Areas.”  To help us prepare, Mr. Feng has sent along this list of facts that every Middle School Student should know.

### Concepts You Need to Know

1.  Angles of a Triangle

• Vertical angles are congruent
• The sum of the measures of the angles of a triangle is 180.
• The measure of an exterior angle of a triangle equals the sum of the measures of the two remote interior angles.

2. Angles of a Polygon

• The sum of the measures of the interior angles of a n-gon is ${(n-2)180}$
• The measure of each interior angle of a regular n-gon is $\dfrac{(n-2)180}{n}$
• The sum of the measures of the exterior angles of any convex polygon, one angle at each vertex, is 360.

3. Triangles

• The length of each side of a triangle must be less than the sum of the lengths of the other two sides.
• If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
• An equilateral triangle has three $60^\circ$ angles.
• Pythagorean Theorem In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the legs.

4.  Areas The area of:

• a rectangle equals the product of its base and height.
• a parallelogram equals the product of its base and height.
• a triangle equals half the product of its base and height.
• an equilateral triangle with side length l is $\dfrac{\sqrt{3}}{4}t^2$
• a rhombus equals half of the product of its diagonals.
• a trapezoid equals half the product of the height and the sum of the bases.
• a circle with radius r is $\pi r^2$ and its circumference is $2 \pi r$.
• a sector AOB of circle O with radius r is $\dfrac{m\angle AOB}{360}\pi r^2$

## Minimal Surfaces and Regular Polyhedron – Recap

Alicia Prieto Langarica continued her tradition of actively engaging the students as they explored deep mathematical concepts. Ms. Langarica began with a discussion of the regular polyhedron and allowed the students to prove for themselves why there can be no more than 5. She then talked about these 5 Platonic Solids and gave some of the cultural context of these important objects.

From this basis, Ms. Langarica was able to describe the wide variety of non-regular polyhedron. As diverse as these objects are, they all have the common properties described by Euler. Ms. Langarica showed how the relationship between the number of vertices, faces and sides would be constant for all of these figures.

To involve the students more directly, the students built their own polyhedron and demonstrated their own diversity and talent. This break activity prepared them for listening to the more challenging portion of the lecture on Minimal Surfaces. Ms. Langarica described the very practical value of finding minimal surfaces to conserve cost or weight in construction projects. She then showed several beautiful examples of minimal surfaces.

By finding the surface normal of any point on a curved shape, Ms. Langarica showed how a minimal surface could be tested or created. To drive this point home, Ms. Langarica took the math circle outside with their polyhedron creations. By dipping these objects into soap bubbles she was able to beautifully demonstrate how minimal surfaces would form spontaneously as a result of the physical properties of the air and soap film.

Ms. Lanagrica has provided her slides from the lecture and answers to the problems. Members of the Metroplex Math Circle e-mail group can download these files from the group site. To join the e-mail group simply click below.

Click to join MetroplexMathCircle

## Minimal Surfaces and Regular Polyhedra

October 11, we will begin with an introduction to polyhedrons and their properties. We will see why there is only a certain number of regular polyhedrons and we will talk about non regular polyherons as well. We will build our own polyhedrons, regular and non regular. Then we will introduce the concept of minimal surfaces and discuss its importance in various fields. The last activity is going to be a fun surprise that will illustrate minimal surface on different shapes.

Ms. Langarica is a mathematics Phd student at The University of Texas at Arlington. She has a BS in Applied Mathematics from the Univestity of Texas at Dallas and was a contestant in the Mexican Mathematics Olympiads for 5 years where she received one national silver medal and two gold medals. Since then, she has been involved continuously in mathematics Olympiads as a trainer and problem writer.