# CC BY-NC-SA

## A Geometric Exploration

A question about angle bisectors Consider a △ABC in which D, E and F are the midpoints of the sides BC, CA and AB respectively. Let G be the centroid of triangle ABC, i.e., the point of intersection of the medians AD, BE and CF. It is well-known that G is also the centroid of triangle DEF. If, instead of being the midpoints, the points D, E and F are the points of intersection of the internal bisectors of

## Problems for the Senior School July 2019

Some problems for the Senior School.

## DIY Problems for the MIDDLE SCHOOL

The tasks of this set require you to get down to some actual cut and paste work. Arm yourself with a chart paper, a roll of cello tape and a pair of scissors.

## Exploring Fractals – The GeoGebra Way

In an article published in the November 2016 issue of At Right Angles we had seen how geometrical fractal constructions lead to algebraic thinking. The article had highlighted the iterative construction processes, which lead to the Sierpinski triangle and the Sierpinski Square carpet. Further the idea of self-similarity within these fractals was reinforced through the recursive and explicit relationships between various stages of the fractal constructions.

## How to Prove It: Contradiction and Contrapositive

In this episode of “How To Prove It”, we consider two similar sounding terms which have great significance in higher mathematics: contradiction and contrapositive. Both of them arise in connection with proofs. We give several examples of proofs of both these kinds.

## Can there be SSA congruence?

If two sides of a triangle have the same lengths as two sides of another triangle, and one angle of the first triangle has the same measure as one angle of the second triangle, what can be said about them? Under what circumstances will they be congruent to one another?

## Exploring Properties of Addition and Multiplication with Integers

This is the third in the series of explorations of the properties of addition and multiplication with different number sets. After considering the set of (i) Whole numbers and (ii) Non-negative rational numbers 1 , in this article we will deal with the integers. This is a good time to reflect on the series − its need and aspiration.

## Fun with Dot Sheets

The ‘TearOut’ series is back, with perimeter and area. Pages 1 and 2 are a worksheet for students, while pages 3 and 4 give guidelines for the facilitator. This time we explore shapes with given perimeter or given area using the dots or the grid.

## Joining the Dots...

In our last Low Floor High Ceiling article, we had looked at Squaring the Dots... a series of questions on counting the dots inside squares of different sizes and orientations drawn on dotted paper with the dots as lattice points. The focus of the activity was to tilt squares and try to find a general formula for the number of dots inside the square of a particular tilt, as the side of the square changed.

## 'CuRe' TRIPLETS

O n observing the triple (25, 125, 225) in which 125 is a perfect cube, 25 and 225 are perfect squares, and the three numbers are in arithmetic progression (AP), I felt that 125 is a very special perfect cube which is guarded by two perfect squares on either side at equal distance.

A surprising discovery we make is that 125 is guarded by two perfect squares in another way, namely: (81, 125, 169); here, 81 and 169 are perfect squares, and the three numbers are in AP as earlier.

## Pages

17914 registered users
6750 resources