# TAG: geometry

#### Quarter the Cross: Connect the Dots

This blog post is about a new variation on the classic Quarter the Cross problem, which I call Quarter the Cross: Connect the Dots.
Background
Here is the original Quarter the Cross problem:

To catch you up, here is everything I’ve written about Quarter the Cross up until now:

Quarter the Cross — in which I first learn about […]

Posted in Isn't maths cool?, One Hundred Factorial | |

#### Quarter the Cross: Colouring

Quarter the Cross is one of my favourite activities of all time, whether in maths or just life. I learned about it way back in 2015 and have been mildly or very obsessed with it ever since. You can read about my obsession in my first Quarter the Cross blog post, and you can read […]

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#### Childhood memories

Two books I’ve read recently have encouraged me to investigate my memories from childhood. In Tracy Zager’s “Becoming the Math Teacher You Wish You’d Had“, she urged me to think about my maths autobiography to see what influenced my current feelings about maths. In Stuart Brown’s “Play“, he urged me to think about my play […]

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#### Book Reading: Which One Doesn’t Belong – Teacher Guide

This is another post about a teaching book I’ve read recently. This one is about the Which One Doesn’t Belong Teacher Guide by Christopher Danielson.
It goes with a beautiful little picture book called “Which One Doesn’t Belong?”, which is a shapes book different from any you’ve ever seen before. In this book, each page has […]

Posted in Education reading | |

#### David Butler and the Prisoner of Alhazen

Once upon a time, I did a PhD in projective geometry. It was all about objects called quadrals (a word I made up) – ovals, ovoids, conics, quadrics and their cones – and the lines associated with them – tangents, secants, external lines, generator lines. During the first two years, I did talks about my […]

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#### The line at infinity: conics

The story so far
I promised Tina on Twitter that I would write about how the line at infinity relates to conics, and I’ve been doing it in the last two blog posts.
First, I talked about what the line at infinity is. We noticed that a set of parallel lines all share a slope, so we […]

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#### The line at infinity: coordinates

The story so far
I made a promise to someone on Twitter to talk about how conics relate to the line at infinity, but when I came to do that, I realised it’s a can of worms that will take a few blog posts to untangle. Last time, I talked about how I construct and think […]

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#### The line at infinity

Why I’m doing this

I foolishly said this on Twitter about a month ago:

@DavidKButlerUoA @MathguyArt on the line at infinity? Tell me about those!
— Tina Cardone (@crstn85) June 14, 2016

At the time I declared this was a bit of a can of worms and I promised to write something and post it later. Well, here it […]

Posted in Isn't maths cool? | Tagged , |

#### Quarter the Cross

At the end of last year, the MTBoS (Math(s) Twitter Blog-o-Sphere) introduced me to this very interesting task: you have a cross made of four equal squares, and you are supposed to colour in exactly 1/4 of the cross and justify why you know it’s a quarter. I call it “Quarter the Cross”.

(The teachers who […]

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