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Eg in definition of 根：ある数を何乗かした数に対するもとの数。

Is it pronounced かず or すう?
CC BY-SA 3.0
2016-06-22T08:31:24.977
36079
2016-07-12T05:38:49.593
15728
question
pronunciation
数 as used in math - pronounced かず or すう?
In everyday conversations, it's always read as かず. But in mathematical
contexts, 数 on its own is usually read as **すう**. すう becomes dominant in math
classes after you graduate from elementary school and start saying things like
these.

>   * 負【ふ】の **数【すう】**  
>  negative number
>   * 複素数【ふくそすう】とは実数【じっすう】 _a_ , _b_ と虚数【きょすう】単位【たんい】 i を用いて、 _a_ + _bi_
> の形で表すことのできる **数【すう】** である。  
>  A complex number is a number that can be expressed in the form _a_ + _bi_ ,
> where _a_ and _b_ are real numbers and _i_ is the imaginary unit.
>

Reading these 数 as かず is not wrong at all, but it sounds less technical.
CC BY-SA 3.0
2016-06-22T12:11:50.013
36084
2016-06-22T13:07:07.397
2016-06-22T13:07:07.397
5010
5010
36079
answer
[数]{すう} is 音読み and [数]{かず} is 訓読み. In general, 音読み of a single kanji itself
does not mean anything while 訓読み is an understandable word. Academic terms are
often read with 音読み.

If a professor reads the difinition to students at his lecture, he probably
read with 音読み. If he is on a TV show and reads the definition to explain the
concept of root, he should read 数 with 訓読み.
CC BY-SA 3.0
2016-07-12T05:38:49.593
36597
2016-07-12T05:38:49.593
16065
36079
answer