# B Fun way of doing multiplication with intersecting lines

1. Mar 19, 2017

### Staff: Mentor

Here's a fun way to do multiplication graphically that originated in Japan:

2. Mar 20, 2017

### phinds

Weirdly interesting.

3. Mar 23, 2017

### Erland

It is of course equivalent to the ordinary multiplication algorithm, just doing it graphically instead of numerically.

4. Mar 23, 2017

### Staff: Mentor

I wonder if some gifted visual learners could do their math this way mentally.

Last edited: Mar 23, 2017
5. Mar 23, 2017

### symbolipoint

Good method to help. I've done that and used the method to show people how multidigit multiplication works.

6. Mar 23, 2017

### Staff: Mentor

It's always interesting to find these alternative multiplication strategies.

Our times tables and method of multiplying is a result of our place value system with the invention of zero.

Whereas the Roman numeral system and earlier systems had to use tables of squares and the formula:

$1/4 ((a+b)^2 - (a-b)^2) = a * b$

$3*5 = 1/4 * ( 64 - 4 ) = 1/4 * 60 = 15$

Or the Trachtenberg system of multiplying using rules to follow for each digit of the multiplier over times tables.

Or the systems created by arithmetic savants with colors and placements that we really don't understand how they do it.

But my favorite was the slide rule where you got an accurate but not exact answer so that close was good enough.