But I can pick any point here;

但我可以在这里任取一点
if I take x to - x,

如果我把 x 换成 -x
the object looks different.

物体就会变化
It looks like that object

它看起来像之前的物体
and relating one object to another object is what I'm trying to do.

而我要做的正是令一个物体与另一个物体重合
I want to relate it to the same object.

我希望这两个物体能够重合
That cannot be done for x.

那么就不能沿 x 轴方向上翻转
It can be done for y;

可以沿 y 方向翻转
for x you've got to do some honest work.

沿 x 轴方我们只能认认真真地计算
The honest work we will do then is to take this thing,

我们接下来要对物体所做的处理就是
take a strip here,

在这里取一小窄条
with location x and width dx,

坐标为 x 宽度为 dx