I will give you some homework problems

我会给你们布置一些作业题目
in which numbers are not put in till the very end,

其中的几道题都得到最后一步再代入数值
or I may not even ask you to put the numbers in,

甚至不需要代入数值
because the thing is to get this formula

因为解题的目的是要导出表达式
because anyone can take the numbers and put them in the calculator.

而谁都会代入数值然后用计算器去算
So, that's going to be part of our agreement

这将是我对各位今后的共同要求
that we will work with symbols.

我们要用符号运算
And if you look at any calculation we do,

如果你看我们所做过的运算
if you caught me in my office,

如果你们正巧看到我在办公室
I'm not putting numbers in very early.

我不会一开始就把数值代入
I mean, I cannot wait to find out what the answer is

我也迫不及待地想要知道答案是什么
but I keep the symbols till the end,

但是我会把这些符号保留到最后