x Turn on thread page Beta
 You are Here: Home >< Maths

# Why does -1 x -1 = +1? watch

1. (Original post by Straw-man666)
Because minus signs indicate a negative entropy change and hence negative energy. It's like antimatter basically and when antimatter collides (multiplication) you get matter (positive energy). This is basically why.

Posted from TSR Mobile
Loooooooooooooooool

Posted from TSR Mobile
2. (Original post by Numberwang)
Because if it wasn't +1, everything would break.

If a number is defined to be where a and b are two real numbers,

we could factor out -a in the right half:

or we could factor out b in the left half:

so you can see and therefore multiplying two negatives gets the same result as multiplying two positives. (so long as you accept two positives make a positive and something multiplied by zero gets zero )
3. (Original post by Kabulkid)
*high five*

hows life? (im expecting an elaborate answer)..
It's getting by.. slowly. Ramadan is going quick though. The weather is superb, so sunny and hot!! Although I'm really thirsty, another 5 hours to go. Time spent on TSR goes so fast like omgg! What upppp
4. [QUOTE=QuantumDuckling;48695154] x QUOTE]

(Original post by james22)
x
No, it doesn't make sense. If I don't have a burger, and my friend also doesn't have a burger, that doesn't make a burger
5. (Original post by Afghan Warrior)
It's getting by.. slowly. Ramadan is going quick though. The weather is superb, so sunny and hot!! Although I'm really thirsty, another 5 hours to go. Time spent on TSR goes so fast like omgg! What upppp
ah thats good to hear, yeah ramadhan is coming to an end what country r u originally from and u doing a-levels/gcse?

im awaiting A2 results so nervy as hell.
6. (Original post by Kabulkid)
ah thats good to hear, yeah ramadhan is coming to an end what country r u originally from and u doing a-levels/gcse?

im awaiting A2 results so nervy as hell.
Parents are born from Pakistan, I'm from here. Don't ask about my username, I'm tired of telling everyone the story behind it. I've just done AS levels, waiting for the results. Proper messed up though, gonna have to resit all the exams, if my sixth form don't kick me out.
Oh, well good luck!! What are you hoping to get?
7. (Original post by Afghan Warrior)
Parents are born from Pakistan, I'm from here. Don't ask about my username, I'm tired of telling everyone the story behind it. I've just done AS levels, waiting for the results. Proper messed up though, gonna have to resit all the exams, if my sixth form don't kick me out.
Oh, well good luck!! What are you hoping to get?
ahh hopefully your results go well for you, why did you mess up?

im hoping to get A*A*A but make dua please i'll make dua as well.
8. (Original post by Numberwang)
Simply because multiplication means how many of the thing you have , for example

5x3 means you have 5 threes or 3 fives

Therefore -1 x -1 means you have negative one negative ones, aka a positive one
If you have a negative neg, you get a positive, the same law as having a positive positive, you get a positive.

I am not "not smart" means I am smart

This is from a student with 100% in all further math modules

Posted from TSR Mobile
9. Aside from axiomatic, definitional explanations, it can be imagined that you have -1 amounts of -1.

Consider that we have 1 quantity of -1. In this case, we simply have -1.

Now consider that we have 0 quantities of that -1. Now we have 0, because we have no -1s. Notice that 0 is greater than the -1 we had originally.

Now we decrease the quantity of -1s we have even more, so that now we say that we have -1 quantities of -1. Now we have even fewer than 0 quantities of -1, so the number that results is again higher than before, and we have 1.

If we have -1 amounts of -1, that is just another way of saying that we have 1.

I'm not sure if other people's imaginations work the same as mine but this is how I imagine it.
10. (Original post by Med_medine)
Simply because multiplication means how many of the thing you have , for example

5x3 means you have 5 threes or 3 fives

Therefore -1 x -1 means you have negative one negative ones, aka a positive one
If you have a negative neg, you get a positive, the same law as having a positive positive, you get a positive.

I am not "not smart" means I am smart

This is from a student with 100% in all further math modules

Posted from TSR Mobile
Best, easiest and most respectful explanation so far, thanks I love using the double-negative for comic effect, so it's great you used it for comparison
11. (Original post by cheeriosarenice)
No, it doesn't make sense. If I don't have a burger, and my friend also doesn't have a burger, that doesn't make a burger
But that analogy is about adding your amount of burgers, and the number of burgers you and your friend have is 0, not -1
12. (Original post by cheeriosarenice)

No, it doesn't make sense. If I don't have a burger, and my friend also doesn't have a burger, that doesn't make a burger
That's addition : -1 + (-1) = -2

Multiplication:

You owe your friend a burger so you have -1 burgers. Your friend becomes a vegetarian (a negative operation) and lets you off the burger you owed him. Now you have 0 burgers so one has been added to your burger collection.

i.e. -1 x -1 = 1.
13. (Original post by Kabulkid)
ahh hopefully your results go well for you, why did you mess up?

im hoping to get A*A*A but make dua please i'll make dua as well.
I encountered some problems throughout the year, in fact ive had them for a few years now. During the year i understood everything but i found it hard to use my time effectively to make sure i dont forget the stuff. And of course with exam stress on top of the other stress it all just got too much to handle for me. Oh well. Everything happens for a reason.
Mashallah, you must be smart! What do you wanna study at uni? And I will do dua for me too please, im really gonna need it!
14. (Original post by Afghan Warrior)
I encountered some problems throughout the year, in fact ive had them for a few years now. During the year i understood everything but i found it hard to use my time effectively to make sure i dont forget the stuff. And of course with exam stress on top of the other stress it all just got too much to handle for me. Oh well. Everything happens for a reason.
Mashallah, you must be smart! What do you wanna study at uni? And I will do dua for me too please, im really gonna need it!
so sorry to hear that, yeah everything happens for a reason, it's all written so don't worry!

thank you haha, inshaAllah i study engineering @ either cambridge or imperial, depending on what I get.
15. (Original post by cheeriosarenice)

No, it doesn't make sense. If I don't have a burger, and my friend also doesn't have a burger, that doesn't make a burger
What's the flaw in my reasoning then?
16. (Original post by Kabulkid)
so sorry to hear that, yeah everything happens for a reason, it's all written so don't worry!

thank you haha, inshaAllah i study engineering @ either cambridge or imperial, depending on what I get.
Check you out, engineering ey :P what kinda engineering?
17. (Original post by Numberwang)
Plot a square -1 by -1 and measure the area.

Geometry is the key to visualising many non-natural numbers.
18. (Original post by james22)
What's the flaw in my reasoning then?
You didn't orde any fries
19. (Original post by Afghan Warrior)
Check you out, engineering ey :P what kinda engineering?
haha thanks

cambridge's course is general engineering and imperial is civil engineering, either one would be amazing tbh but still, cambridge is cambridge
20. (Original post by scrotgrot)
Plot a square -1 by -1 and measure the area.

Geometry is the key to visualising many non-natural numbers.
Doesn't work, plot a 1*-1 square and measure the area.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: July 24, 2014
Today on TSR

### Four things top students are doing

Over the Easter break

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams