But we know another vector that is also perpendicular to the level set of g. That is the gradient of g.

但我们知道有另外一个向量也是和g的等值面垂直的，这个向量就是g的梯度。

youdao

Then you know that the gradient of g is perpendicular to the level surface.

那么就知道了g的梯度,是垂直等值面的。

youdao

That means that the gradient of f is perpendicular to the level set of g.

也就是说f的梯度向量,应该与g的水平集垂直。

youdao