This is the level curve maybe f equals something.

这个就是f等于某个数字的等高线。

youdao

Do you mean how do I know that it is perpendicular to a level curve?

你想问的是，我如何知道它是和等高线垂直的吗？

youdao

So, the level curve corresponding to zero is actually two diagonal lines.

0的等高线实际上是两条对角线。

youdao

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