Cube Roots From Scam School

Published on Thursday, March 21, 2013 in , , , , ,

Scam School logoScam School has just covered one of my favorite mathematical feats of all time!

Doing cube roots in your head is a skill that seems very impressive, but as you'll see in the video, you can learn the basics and start praciticing in less than 10 minutes.

If you take a number x and multiply by itself two more times, x × x × x, or x3 (x cubed), then x3 would be referred to as the cube of x, and x would be referred to as the cube root of x3. For example, since 3 × 3 × 3 = 27, we say that 27 is the cube of 3, and conversely that 3 is the cube root of 27.

Now that we're clear on the terminology, here's the Scam School episode about doing cube roots in your head:

Over at the Mental Gym, I've had a post explaining this feat for quite some time. Once you feel confident doing cube roots in your head in this manner, you can move on to 5th roots! The approach is similar, but strangely, doing 5th roots is actually easier than cube roots!

Once you master squaring numbers ending in 5, you can even handle square roots in a similar manner, as well.

I've always thought it was somewhat amusing that lower roots were more challenging to approach than higher roots with this approach.

How far have people taken this approach? There are several people who have practiced finding the 13th root of a 100-digit number, and beyond! For a feat like this, any time under 2 minutes is considered an excellent time. It is, of course, far more challenging to turn this one into an entertaining bar stunt.

Practice this one and have fun displaying your new-found skill for your friends!

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