Here’s a blog post I wrote on this: http://mindyourdecisions.com/blog/2012/01/27/multiplicating-with-lines-math-trick-how-it-works/
Many people asked me to write a reference guide. So I wrote a book “Multiply Numbers By Drawing Lines.” https://www.amazon.com/gp/product/1500866148/
I’ve made a few follow-up videos you might like.
Multiply by lines (advanced examples)
Multiply by lines (why it works)
Multiply by lines (the rotation trick)
Send me suggestions by email (address in video). I consider all ideas though can’t always reply!
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