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Why is $1$ not considered a prime number? Or, why is the definition of prime numbers given for integers greater than $1$?

Feb 3, 2021 · Hi, welcome to Math SE! Can you show us the proof you're looking at? There are a lot of false proofs of this sort out there, typically involving division by 0, I would imagine that's probably the …

知乎，中文互联网高质量的问答社区和创作者聚集的原创内容平台，于 2011 年 1 月正式上线，以「让人们更好的分享知识、经验和见解，找到自己的解答」为品牌使命。

Is there a formal proof for $(-1) \\times (-1) = 1$? It's a fundamental formula not only in arithmetic but also in the whole of math. Is there a proof for it or is it just assumed?

如何在输入法里输入这个符号？Google了很多发现都不对

Substitute a by 1 and b, c by x, we find both definition of 1 x and x − 1 reduce to the unique y in Y (if exists) such that yx = 1 = xy. As a result, 1 x = x − 1 whenever they make sense.

把 里面的“/” 理解为将投注额平分。 比如你打算投注10块的让0.5/1， 就是5块买 让0.5 剩下5块买让1 如果让球方净胜1球，那么让0.5的5块你赢了，让1的5块不输不赢，总的就赢一半 如果让球方净胜2球及 …

40 10 I need to format these numbers so that they form the sum 1, but they should keep their "weight". In this specific case: 40 would become 0.80 10 would become 0.2 But if I have more values (like 40, …

红线是n-1到n的割线，绿线是n处的切线 图像上显然，割线的斜率大于切线的斜率。 所以我们有割线的斜率 \dfrac {\ln \left ( n\right) -\ln \left ( n-1\right) } {n-\left ( n-1\right) } 大于切线的斜率 \left ( \ln n\right) …