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/sci/ - Science & Math

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6910066 No.6910066 [Reply] [Original]

ITT: post useful math hacks & tricks

>> No.6910067
File: 34 KB, 640x404, percenthack.jpg [View same] [iqdb] [saucenao] [google]
6910067

>>6910066

>> No.6910082
File: 76 KB, 1000x1179, #lifehack.jpg [View same] [iqdb] [saucenao] [google]
6910082

>>6910067
Alternatively you could just calculate 0.4 * 300 = 4 * 30 = 120
#HacksOnLife

>> No.6910085

>>6910066
Are you implying you need a "hack" to remember what the greater-than sign means?

>> No.6910093

>>6910085
I usually forget my arthritic and these pictures are a great help.

>> No.6910136

OP here, post more math hacks lads

>> No.6910142

>>6910085
remember this is /sci/

>> No.6910164

>>6910082
>out of clean spoons?
>wash a fucking spoon
>and while you are at it wash all of the dishes
>and clean your kitchen and the rest of the fucking house
>fucking pig

>> No.6910168

>>6910066
Density of the reals
Arbitrary neighborhoods
Surjective mappings
Terry Tao's cock

>> No.6910169
File: 26 KB, 480x512, d33c1909-785d-44a6-89cb-ed7cfa76c74f.jpg [View same] [iqdb] [saucenao] [google]
6910169

>> No.6910170
File: 21 KB, 604x615, math mindfuck.jpg [View same] [iqdb] [saucenao] [google]
6910170

>> No.6910173

>>6910170
yeah man I'm so fucking mad right know

>> No.6910182

>>6910168

explain (srs)

>> No.6910220

>>6910169
WOOW

>> No.6910232

>>6910170

Even without being a mathmatician I can tell that this entire proof is just exploiting how imprecise we can be with repeating digits and rounding.

9.9 repeating times 10, if we just look at the digits past the decimal point, can't be the same value as the digits past the decimal point in 9.9 repeating, because every time you multiply it by itself the value shrinks a little further away from itself, because it is a fraction of 1.

I feel like I just got trolled into wasting effort on this, feel free to laugh at me.

>> No.6910243

>>6910232
so are you a mathematician or not ? post some tricks to become one pls

>> No.6910263

>>6910243

I'm not, sorry dude.

>> No.6910267

The whole crocodile sign didn't make sense to me. It seems natural that the big number eats the small number, not the other way around.

>> No.6910274

>>6910267
what it means is that the greedy crocodile would want to eat the bigger cake, hence point its mouth towards the bigger one.

>> No.6910279

>>6910274
wouldn't he prefer food that fit in his mouth

>> No.6910291

Am I the only one in the world who never had trouble remembering the difference between greater than and less than?

>> No.6910296

>>6910279

The crocodile can take multiple bites

>> No.6910303
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6910303

I learned this trick in graduate level algebra. Shit blew my mind.

>> No.6910304

>>6910067

100% of 300

>1*30

>> No.6910306

>>6910169
mine did

>> No.6910315

>>6910304
the 10s digit of 100 is 10. 10x30 = 300

>>6910169
>>6910303
what shit elementary schools did you go to where they didn't teach you this?

>> No.6910316

>>6910303
This is literally <span class="math">(a+b)^2 = a^2 + 2ab + b^2[/maths] isnt it?[/spoiler]

>> No.6910319

>>6910316
This is literally <span class="math">(a+b)2=a2+2ab+b2[/spoiler] isnt it?*
Sodding americans

>> No.6910323

>>6910316
>>6910319
yes, basically

also
<span class="math">(a+b)^2 = a^2 + 2ab + b^2[/spoiler]
is that so hard?

>> No.6910326

>>6910323
Didnt realise the ^'s were left out when I copied it

>> No.6910358

>>6910169
How little deductive can you be that you don't see this on your own? No one needs to teach you that

>> No.6910537

>>6910169
this shouldnt be taught
if you're too much of an idiot to not notice this there is no hope for you in mathematics

>> No.6910571

>>6910169
Why would you need to be taught this?

>> No.6912378

>>6910319
God why are British people so bad at math.

>> No.6912384

Is this a cringe thread?

>> No.6912647

>>6910169
both digits also all add up to 9

>> No.6912700

>>6910067
>Not multiplying 0.4 by 300 which is just equal to 4*30, but better and more precise.

>>6910169
They did and I didn't endorse it. All I do is multiply the second, non-9 number by 10, and then subtract it from itself in my head. I never memorized any of the multiplication table shit, so I had to do it all the time and became pretty good at it.

tl;dr - This is shit. Multiply the non-9 number by 10 and then subtract it from itself.

>> No.6912709

>>6910232
It's the whole 0.999... = 1 /sci/ maymay expressed in some leddit tier rageface fashion.

>> No.6912722

>>6910291
Nope. This is just /sci/ shitposting.

>>6910303
>Graduate level algebra
Are you literally 16?

Also, you can just 6(61*10) or 10(61*6) and then add a 61.

>> No.6912757

>>6910170
>>6910232

Personally I always love self-imposed darwinism. Basically, people come in here, prove how they can't do junior elemetary math, and then use that lack of knowledge to prove how .99 = 1. My sides go haywire every single time. :)

Nothing is more amusing than stupid people doing make believe about being smart. And the world is filled with such people.

Protip: Trolls are an obvious part of that same subgroup.

>> No.6912778

What a shit thread. Most of it is either unnecessary if you actually use math, like the greater than thing, or shit you should have deduced by yourself unless you are a retard, like the x9 thing.

>> No.6912787

>>6910066
Not really a trick and more of a physics thing, but it's good to remember that polar coordinates exist and sometimes make your life so much easier.

>> No.6913447
File: 18 KB, 500x318, multiply.png [View same] [iqdb] [saucenao] [google]
6913447

I successfully completed my bachelor's before this was shown to me

>> No.6913470

>>6910067
45% of 90 000 = 40500
4 * 9000 = 36000

wow much math such hack very planet

>> No.6913487

>>6910303
You learned how to use the distributive property in graduate level algebra?
Are you retarded or just lying?

>> No.6913492

>>6910067
I just figure out what 10% is and multiply it by however many tens there are.

>> No.6913494

>>6910169
Why did the teacher need to point that out to you?

>> No.6913514
File: 9 KB, 441x285, whut.png [View same] [iqdb] [saucenao] [google]
6913514

Inequality signs originate from the arrows of the number line

A < B
means A is found to the left of B of the number line
A > B
means A is found to the right of B of the number line

"B" is the reference point

40% of 300
%=1/100 so
40/100*3*100
40*3

>>6913447

>> No.6913520

>>6913514
*endpoint arrows of the number line

There's a lot more math hacks taught in common core, like partial quotients, I really wish it was widely embraced in the US

>> No.6913527

The other day out while working with scalars that if I were to take two scalars, a and b for example, and add them together by standard scalar addition, then starting with a and then adding b to it is the exact same as starting with b and then adding a to that. So it's almost like a + b = b + a. But here's the real trick. I realized I could do this for 3, or even 4 numbers at a time if I really tried hard. I am fairly certain this implies that the order which I multiply numbers doesn't actually change their sum. Have yet to see a solid proof of this, may create one and submit for Nobel prize. Thank you very much.

PhD. Harvard Mathematics professor here btw.
Discovered this fact in my graduate level pre-algebra class.

>> No.6913530

http://everydaymath.uchicago.edu/teaching-topics/computation/

>> No.6913533

Here's a trick that me and my colleagues use to solve elementary algebra:

Use a fucking calculator.

>> No.6913539

>>6913533
>be in algebraic topology class
>teacher says the calculator doesn't know the answer anymore
>I never learned how to lift homotopic paths without a calculator

>> No.6913588

>>6913539
>he can't compute homotopy groups on his TI-98

>> No.6913613

on a side note, does this line of thinking has merit with the repeating decimals issue?

Let's assume 0.99... = x has n decimal places
normally 10x would have n-1 decimal places
and (10x - x) / 9 = x would yield a 0.00...1 for a finite n
if we do the same operation in a limit with n tending towards infinity and obtain something like 0.00....1 ~ dx, which is proven not to exist, would we have shown that this line operations are invalid?

>> No.6913622

>>6913539
Lel'd out of 10

>> No.6913802
File: 6 KB, 113x120, 113px-HomotopyLiftingProperty-02.png [View same] [iqdb] [saucenao] [google]
6913802

>>6913539
Do you even lift?

>> No.6913923

>>6910170
you troll, 1/(infinity) would represent the concept of the smallest value between 0 and 1. 1-0.000...0001=.9999...
1-1-0.000...0001=.9999... -1
or
1=.9999...
.00..001=0
1/infinty=0 so...
infinity=1/0 YoU JuSt BLeW My MiNd

>> No.6913972

<span class="math">$\overline{x+3)x^4+10 x^3+35 x^2+50 x+24}$[/spoiler]

Long division. It helps tons when no calculator.

>> No.6913976

>>6913972
Hahahahahahahahahahahahahahahahahahahahahahahahahahahahaha
nice TeX <span class="math"> faggpt[/spoiler]

>> No.6913987

>>6910170
>posting a basic GCSE maths proof
>Mfw umad?

>> No.6913992

>>6913976
<span class="math">e^{at}shit(f_{aggot})[/spoiler]

>> No.6914003

>>6913992
:^(

>> No.6914042
File: 167 KB, 360x160, Fourier square wave.gif [View same] [iqdb] [saucenao] [google]
6914042

This is explains Gibbs phenomenon if you look at the spikes at the end of each wave.

>> No.6914061

>>6913802
My sides seem to have undergone an inversion