- #1

- 1,384

- 2

## Main Question or Discussion Point

Mathematica:

Why does it do this? Wolfram Alpha gives the answer I expected:

http://www.wolframalpha.com/input/?i=d%2Fdu+%28{%28u+%2B+2+v%29%2F3%2C+%28u+-+v%29%2F3%2C+w}%29

{1/3, 1/3, w’(u)} = {1/3, 1/3, 0} if w doesn't change with u.

Code:

```
In[1]:= x = {(u + 2 v)/3, (u - v)/3, w}; D[x[u], u]
Out[1]= {1/3, 1/3, 0}[u] + {(u + 2 v)/3, (u - v)/3, w}’[u]
```

http://www.wolframalpha.com/input/?i=d%2Fdu+%28{%28u+%2B+2+v%29%2F3%2C+%28u+-+v%29%2F3%2C+w}%29

{1/3, 1/3, w’(u)} = {1/3, 1/3, 0} if w doesn't change with u.