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First Instructable, hope you like it.
Math. Love it or hate it, everyone must do it at some point in their lives. Some of us revel in numbers and equations and have a passion for math. This Instructable is for you, oh math lovers of the world.
This Instructable describes mental cube-root extraction: a cool math trick you can do to amuse and amaze your friends, and score some mean cubicle-cred with your fellow geeks. I can accept no responsibility for the social implications of using this skill (but then, as a geek, you probably already treat social implications of your geekiness with abandon, so it's all good).
At any rate, let's move on!
Update: Featured?!? Thank you so much Instructables, that means alot to me :-)
Update2: I know it's alot to ask from you folks, but please, vote for this in the book contest if you think it's cool. I would really appreciate that.
Math. Love it or hate it, everyone must do it at some point in their lives. Some of us revel in numbers and equations and have a passion for math. This Instructable is for you, oh math lovers of the world.
This Instructable describes mental cube-root extraction: a cool math trick you can do to amuse and amaze your friends, and score some mean cubicle-cred with your fellow geeks. I can accept no responsibility for the social implications of using this skill (but then, as a geek, you probably already treat social implications of your geekiness with abandon, so it's all good).
At any rate, let's move on!
Update: Featured?!? Thank you so much Instructables, that means alot to me :-)
Update2: I know it's alot to ask from you folks, but please, vote for this in the book contest if you think it's cool. I would really appreciate that.
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Signing UpStep 1A Note on Limitations
The technique I describe in this Instructable has a few important limitations that you should be aware of.
So, here they are:
1) This trick only works for perfect cubes, it will not work for any arbitrary 6-digit number
2) The cubed number must be an integer (whole number) between 0 and 100 (or 0 and -100). No fractions, no decimals.
For ways to expand the technique, see the last step of the instructable.
So, here they are:
1) This trick only works for perfect cubes, it will not work for any arbitrary 6-digit number
2) The cubed number must be an integer (whole number) between 0 and 100 (or 0 and -100). No fractions, no decimals.
For ways to expand the technique, see the last step of the instructable.
| « Previous Step | Download PDFView All Steps | Next Step » |
1. we get the digit sum of a no. by "adding across" the no. For instance, the digit sum 0f 13022 is 8.
2. we always reduce the digit sum to a single figure if it is not already a single fig.
3 .In "adding across" a no. we may drop out 9's. Thus if we happen to notice two digits that add up to 9, such as 2 and 9, if we ignore both of them; so the digit sum of 99019 = 1 at a glance.(If we add up 9,s we get the same result)
4. because :nine don't count" in the process, as we saw in3 step, a digit sun of 9 is the same as a digit sum of zero. The digit sum of 441,e.g = 0.
You may use this for Multiplication, Cubes , Squares etc.
you may also check weather your squared no, is correct or not.
I will explain it:-
take an example for 207.
square(207)= 42849
now add digits of LHS and RHS separately. we get
Sq(2+7) = 18
Sq(0) = 18
0=2+7
0=9
0=0
thus your calculation is correct.
take another example.
Sq(897) = 804609
sq(6) = 18
36 = 180
0=0.
http://www.instructables.com/id/Square_2_Digit_Numbers_Mentally/
http://www.instructables.com/id/Square_2_Digit_Numbers_Mentally/
Hope you like it :-)
http://www.instructables.com/id/Square_2_Digit_Numbers_Mentally/