6.5 方向微分

1.

(a) $ \displaystyle{-\sqrt{2}}$ (b) $ \displaystyle{-\frac{e}{\sqrt{2}}}$

2.

(a) $ \displaystyle{\sqrt{3}}$ (b) $ \displaystyle{1}$ 

3.

(a) $ \displaystyle{\frac{3}{\sqrt{10}},  (0,1)}$(b) $ \displaystyle{-\frac{6}{\sqrt{10}},  (0,-1)}$