z I do F dot n. That just gives me the z component which might involve x, y and z.
把F和n做内积，于是得到,它由x，y，z组成。
Remember, partial f, partial x was obtained by y That means I am slicing the graph of f by a plane that is parallel to the x, z plane.
要记得，在这里的fx中,是作为常量保持不变的。，looking，at，the，situation，where，y，is，held，constant。,这是我用一个平行于xz坐标系的平面,横截了f，所得到的图形。
The power of linearity is F=k1+k2 if I come across f of x, y, z equals k1 plus k2, if it is a linear equation, I don't have to go and solve it all over again.
线性的威力是,一个方程，如果它是个线性方程，那么我就不用再去解他了。
Then I switched on a projector that flashed the letters F, Z and B on a screen.
然后，我打开一台投影仪，在一个屏幕上闪出了字母F、Z和B。
Then I switched on a projector that flashed the letters F, Z and B on a screen.
然后，我打开一台投影仪，在一个屏幕上闪出了字母F、Z和B。
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