Why is negative times negative positive? PART I (James Tanton)

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Why is negative times negative positive? PART I (James Tanton)

Рет қаралды 38,754

Күн бұрын

Mathematics Video
This is the first half of a short video explaining, in true and honest and accessible terms, why negative times negative is positive. At last!

Пікірлер: 30

@volvol1 10 жыл бұрын

That was a really great explanation. Ah, the JOY OF LEARNING, of insight!!!

@alittax 2 жыл бұрын

Indeed, it is a great sensation. :)

@hasnaa7316 2 жыл бұрын

YOU'RE AWESOME i've been looking for the explanation behind this for a long time thank you.

@adamzheng4362 7 жыл бұрын

2:20 It makes sense because -3 groups would, essentially, be repeated subtraction from zero, which is 0 - 5 - 5 - 5= -15

@abdulhakkim3947 2 жыл бұрын

U r awesome 👏

@rhoadess 11 жыл бұрын

I tried mirror reflections upon the number line? kinda works. So think of (-1*) as a operator that reflects a number to the opposite direction. If you do this an even number of times, you end up in the original direction.

@aidenayyash8067 3 жыл бұрын

thx man i understood it easily

@edwardschneider7035 9 жыл бұрын

yet you failed to explain why; you start with an assumption but never explain why the assumption is valid

@TheBasikShow 7 жыл бұрын

Really just because the extension makes sense. It feels nice for things to be commutative (AxB=BxA) and distributive (Ax(B+C)=AxB+AxC, which is basically what he's doing with the rectangles). As in a lot of math, the axioms we use are flimsy, but the ones most people use are the ones intuitive to us. The assumption is valid because we /say/ it's valid, and we say it's valid because we like patterns to stay the same.

@KKKK-jr1nm 4 жыл бұрын

@@TheBasikShow thanks for explaining!!

@leonardschrock380 5 жыл бұрын

This is interesting. My thinking on this question is quite different. If I change a sign in a multiplication problem, then the sign of the answer must change. All plus numbers multiplied give a plus answer. If you change one number in the problem then the sign of the answer changes to minus. If you change two signs in the problem then the two changes of the answer sign will come back to positive. More numbers work as well. (-2)x(-2)x(-2)=(-8).

@MrBrix3 6 жыл бұрын

awesome explanation...........Thanks so much

@ikemuoma8495 4 жыл бұрын

Nicely done. 👍👍

@Picasanta 11 жыл бұрын

My God!!! Thank you very very much!

@annabizaro-doo-dah 5 жыл бұрын

Thumbs up for the visual representation of the two posative groups of numbers from different visual perspectives.

@Bredrin90 11 жыл бұрын

Dr. Tanton: Thanks for these great videos and the great PD on "Exploding Dots"!

@MrBrix3 6 жыл бұрын

Headed to your website!!!!

@1DARBY1 9 жыл бұрын

Great explanation thanks

@whiteaccau 14 жыл бұрын

Very helpful, thanks.

@DrJamesTanton 13 жыл бұрын

@curvaceousss Thanks! - J

@lilmizawesome1 12 жыл бұрын

you rock! This video helped a lot!

@2001mathnerd 10 жыл бұрын

well done sir.

@catirerubio 4 жыл бұрын

You seem to be pulling numbers out of the air then creating plus or minus numbers to make them work via the square. Why cannot you use the original numbers in the formula? This does not compute.

@GrandTheftAutowkthru 7 жыл бұрын

Think of +ve and -ve Numbers like Mountains where +ve numbers go up and -ve Numbers go down Say your mountain have height of 5000 or +5000 when you MULTIPLY -1 or ( -1 - 1 -1 .... ) 5000 times Your Mountain gets Inverted and looks like the letter n that a letter u When you times -1 again it goes up to a u (-1) * (-1) = 1