人们通常直接在桌布上切面包，而不是在盘子上。

People often cut bread directly on a table cloth rather than on a plate.

youdao

在这点上，我们有一个切于等值面的切面，这就是等值面的切平面。

And, at this point, I have the tangent plane to the level surface OK, so this is tangent plane to the level.

youdao

但如果切面取在最前方附近，实际上，积分域。

But, if I take a slice that, say, near the very front, then in fact, only a very small segment of it will be in my region.

youdao