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# Maths illusions watch

1. here's a thread where you can post the best maths illusions. Please feel free to post illusions.

Here's mine. tell me what you think of it

a = b
times both sides by b
ab = b2
minus a2
ab – a2 = b2 – a2
factorise
a(b-a) = (b+a)(b-a)
divide by (b-a)
a = b+a
replace b by a
a = a + a
a = 2a
divide by a
1 = 2

If 1 = 2, the world would end
2. oh dear.
3. Dear oh dear.
4. Haha, quite good.
5. (Original post by mockel)
Dear oh dear.
This should be moved to GC, like you suggested, to amaze the commoners.
6. (Original post by endeavour)
This should be moved to GC, like you suggested, to amaze the commoners.
It probably should. I have used it to amaze some rather stupid people in my class before . I dont expect anyone here to fall for it.
7. Mathematical proof that women are evil???

Women take time and money, so:
Women = Time x Money

Any decent businessman will tell you time is money:
Women = Money x Money

Money is the root of all evil:
Women = √Evil x √Evil

But if you mulitiply a square root by it's own square root you get itself, so:
Women = Evil
8. If you replace b with a then you're putting a different number in, right?

I'm gonna sound so stupid but I don't get it the thing doesn't make sense...

and no I'm not dumb I'm just unbelievably CRAP at Maths.
-1 = -1
1/-1 = -1/1
sqrt(1/-1) = sqrt(-1/1)
1/i = i/1
1 = i^2
1 = -1

10. (Original post by corkskrew)
Mathematical proof that women are evil???

Women take time and money, so:
Women = Time x Money

Any decent businessman will tell you time is money:
Women = Money x Money

Money is the root of all evil:
Women = √Evil x √Evil

But if you mulitiply a square root by it's own square root you get itself, so:
Women = Evil
Men cost time and money too! - so using your logic: Men = Evil

Men : Women
Evil : Evil
Which cancels each other out

You see, men and women - it's meant to be - they're complimentary!
11. (Original post by irisng)
If you replace b with a then you're putting a different number in, right?
my first line was a=b, so no.
12. (Original post by irisng)
Men cost time and money too! - so using your logic: Men = Evil

Men : Women
Evil : Evil
Which cancels each other out

You see, men and women - it's meant to be - they're complimentary!
I would say women take much more time and money up then men.
Men = time x money = money x money = √evil x √evil = evil
Women = time² x money² = money² x money² = evil x evil = evil²

Basically to cure world poverty kill women.
13. (Original post by Zuber)
I would say women take much more time and money up then men.
Men = time x money = money x money = √evil x √evil = evil
Women = time² x money² = money² x money² = evil x evil = evil²

Basically to cure world poverty kill women.
Well I suppose that would in effect terminate the human race

Women tend to give a lot more into a relationship though, generally speaking - so it cancels everything out again.

And I'm sure there're some men who won't thank you for killing all women
14. Men are more evil than women...
Attached Images

15. well science has been developing techniques to make babies from 2 men or women. (i.e. fuse 2 ova nuclei or 2 sperm nuclei and insert into an enucleated egg). so we probably wouldnt be terminated.
And women tend to give more in a relationship??? utter lies. on the whole men and women give into relationships equally.
16. (Original post by irisng)
If you replace b with a then you're putting a different number in, right?

I'm gonna sound so stupid but I don't get it the thing doesn't make sense...

and no I'm not dumb I'm just unbelievably CRAP at Maths.
I'll give you a (big) hint: the problem occurs when dividing through by (b-a).
17. (Original post by Zuber)
here's a thread where you can post the best maths illusions. Please feel free to post illusions.

Here's mine. tell me what you think of it

a = b
times both sides by b
ab = b2
minus a2
ab – a2 = b2 – a2
factorise
a(b-a) = (a+b)(a-b)
divide by (b-a)
a = a+b
replace b by a
a = a + a
a = 2a
divide by a
1 = 2

If 1 = 2, the world would end
there are three very obvious stupid mistakes with this. firstly you've factorised wrong. here's the corrected version:
ab - a² = b² - a²
a(b - a) = (b - a)(b + a)
at this line you had (a - b)(b + a)

now of course, you can tell me that a = b and hence you can have b - a. well, ok let's pretend that you're right and continue with your method.

so we have a(b - a) = (a - b)(b + a)
you want to divide by (b - a). well you can't. if a = b, then b - a = 0, and you cant divide by zero. but you have, hence the answer is undefined.

well let's continue anyway.
a = 2a
divide by a: 1 = 2. this can't exist, hence a must equal zero and hence a = 2a.

without being harsh, i suggest you relearn your basic algebra, because you've made some very simple mistakes and it'll be quite easy to fix.

i'll post some interesting maths after i get back from this morning's tripos exam (which, funny enough, is maths).

edit: mop's beaten me to the correct answer another cambridge genius i've realised i can't even post what i wanted to because they don't have the correct symbols so i'll post in words
e^i(theta) = cos(theta) + isin(theta)
woo
which gives my fave equation
e^i.pi +1 = 0
19. (Original post by Lozza)
there are three very obvious stupid mistakes with this. firstly you've factorised wrong. here's the corrected version:
ab - a² = b² - a²
a(b - a) = (b - a)(b + a)
at this line you had (a - b)(b + a)

now of course, you can tell me that a = b and hence you can have b - a. well, ok let's pretend that you're right and continue with your method.

so we have a(b - a) = (a - b)(b + a)
you want to divide by (b - a). well you can't. if a = b, then b - a = 0, and you cant divide by zero. but you have, hence the answer is undefined.

well let's continue anyway.
a = 2a
divide by a: 1 = 2. this can't exist, hence a must equal zero and hence a = 2a.

without being harsh, i suggest you relearn your basic algebra, because you've made some very simple mistakes and it'll be quite easy to fix.

i'll post some interesting maths after i get back from this morning's tripos exam (which, funny enough, is maths).

edit: mop's beaten me to the correct answer another cambridge genius i've realised i can't even post what i wanted to because they don't have the correct symbols so i'll post in words
e^i(theta) = cos(theta) + isin(theta)
woo
which gives my fave equation
e^i.pi +1 = 0

the math man is here
numbers war started
20. (Original post by Mop)
haha ok, didn't realise he actually knew he was being dumb. it really does look like something my little sister would write down tho

oh i really hope there's a nice matrix question today.

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