第 10 条 · 用字母代表一般数

All this is evident; and we have only to mention, that in Algebra, in order to generalise numbers, we represent them by letters, as a, b, c, d, &c.

这些都很明显；我们只需要补充一点：在代数中，为了把数一般化，我们用字母来表示它们，如 a、b、c、d 等。

Thus, the expression a + b, signifies the sum of two numbers, which we express by a and b, and these numbers may be either very great, or very small.

因此，式子 a + b 表示两个数的和；这两个数用 a 和 b 表示，它们可以很大，也可以很小。

In the same manner, p + m + b + x, signifies the sum of the numbers represented by these four letters.

同样，p + m + b + x 表示由这四个字母所代表的数的和。

If we know therefore the numbers that are represented by letters, we shall at all times be able to find, by arithmetic, the sum or value of such expressions.

所以，如果我们知道这些字母所代表的具体数，就总能用算术求出这类式子的和或值。