Name: 操作の順序が間違っている (The Order of Operations is Wrong)
Uploaded: 2021-01-14T10:21:01.000Z
Duration: 4 min 11 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

仮定法過去

If you went to elementary school in the United States (or much of the rest of the world)

様態の副詞

you almost certainly learned about something boringly called the "order of operations"

- a set of rules for whether or not you should do multiplication before addition or addition

before subtraction to get the right answer on your math test.

Except, you don't always get the right answer, or even, one answer - I mean, is 8-2+1 equal

to 5 or 7? and is 6/3/3 equal to two thirds or six? - the problem is, focusing on the

order of operations can lead to ambiguity and obscures the real, underlying, and often

A mathematician will tell you that 8-2+1 is really 8+(-2)+1, which is unambiguously equal

to 7, even though the so-called "order of operations" standard in the US tells you the

answer is 5. If you want five for your answer, then you really need some parentheses!

But why is this ambiguity even possible? Because fundamentally, all of these operations are

simply different procedures that start with two numbers and combine them in some way to

give you a single number. Each operation takes two numbers as input - two, and no more. If

you want to be entirely unambiguous (and pedantic), every single pair of numbers in an algebraic

expression should be inside parentheses, and then there's no need to know ANY order of

operations - just evaluate the innermost parentheses first, and work outwards, collapsing them

down pairwise like a championships bracket.

But it turns out that's not the only way - it's possible to CHANGE the order in which you

do the operations, to rearrange the parentheses, as long as you know what the underlying mathematics

For example, if you want to add (3+4) and then multiply the result by 5, you can either

do the addition first and get 7 times 5 = 35, or you can do the multiplication first as

long as you know that multiplication "distributes" across all the terms in the parentheses...

that is, (5*3) plus (5*4) = 15 plus 20 = 35 - the same answer! And how do we know multiplication

distributes? One way is to draw rectangles... but I've done that before.

The same rearranging can be done for exponentiation and multiplication: (3*2) all squared (or

6^2=36) is the same as 3 squared times 2 squared - 36; It even works for addition and subtraction:

So, the true order of operations is this: use parentheses, and learn what exponentiation,

multiplication, addition and the rest are REALLY doing - then you can proceed however

That's not to say that we don't have a conventional order of operations in mathematics... I mean,

deciding that we evaluate multiplication before addition allows us to get rid of lots and

lots of redundant parentheses, and noticing that (1+2)+3 = 1+ (2+3) and 2*(3*4)=(2*3)*4

removes a ton more... but the point is that those parentheses are still there, still implied

- just like how 3 minus 4 is secretly implying 3+ negative 4 and 3 divided by 4 is really

3 times one fourth. But any time the result might be ambiguous, you really need to use

parentheses. Then you can proceed in whatever order you want.

The order of operations learned in school, however, is different - it's a mechanical

set of instructions that dictates just one of many ways you can do algebra - it locks

you into a single path through the beautiful mathematical landscape, which, while necessary

for a computer whose goal is merely to give you the right answer, doesn't really give

any insight onto WHAT IT IS that you're doing when you do algebra.

So, while, the order of operations isn't technically wrong, because most of the time it'll give

you the right answer, it's morally wrong, because it turns humans into robots.