Prove identity

1. Dec 19, 2011

matematikuvol

1. The problem statement, all variables and given/known data
$$\frac{\partial \vec{r}}{\partial q_i}gradf(r)=\frac{\partial f(r)}{\partial q_i}$$

2. Relevant equations
$$gradf(r)=\frac{df}{dr}gradr=\frac{df}{dr}\frac{ \vec{r}}{r}=\frac{df}{dr}\vec{r}_0$$

3. The attempt at a solution
$$\frac{\partial \vec{r}}{\partial q_i}\frac{df}{dr}\vec{r}_0=?$$
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution