# The best way to multiply!

by Domino83
Tags: multiply
 P: 1 I've got a very helpfull system for making calculations, more exactly: multiplying. How do you calculate large multiplications like e.g. 1538x483 Takes some time, isn't it? Well, I found this system for solving the problem and it's great. Whatch this, amazing: http://www.metacafe.com/watch/308408...iplying.%20Don Greetz Domino Edit: I see it has been removed today... strange.
 Emeritus Sci Advisor PF Gold P: 7,337 What I see is just a complexification of normal multiplication. Whats the point?
 P: 223 I'm sorry, but this is pretty stupid ... This is merely obfuscation of the normal polynomial time, grade-school multiplication. If you want some "amazing" systems for mulitplying large numbers, look up the divide-and-conquer selection algorithm, or Fast Fourier Transforms. Or, for a system that is doable by hand use the system Al Khwarizmi discovered, one that is used today in some European countries. It works by synthesizing a binary-styled multiplication. You multiply and divide number a and number b, respectively, by 2, then strike out the even rows and add up column b. I won't bother showing how it works, because this is utterly pointless. The point being, that the technique outlined in that video is nothing but a rewrite of the grade-school algorithm, and nowhere near "the best way to multiply large numbers".
 HW Helper P: 1,025 The best way to multiply! I like to use the FOIL method for multiplication of 2 or 3 digit numbers, e.g. 79x91=(80-1)(90+1)=7200+80-90-1=7189 which is not very fast, but I don't care to memorize much of my times table, so it helps me.
Emeritus
$$79\times 91=(85-6)(85+6)=85^2-6^2=7225-36=7189$$