# Homework Help: Quick Guass's Law of Gravitation Clarification

1. Apr 11, 2013

### bmb2009

1. The problem statement, all variables and given/known data

The picture attached shows the answer to a sample problem... I don't understand the last step... how does ∇g = C (1/r^2)∂/∂r(r^4) ??? where did the r^4 come from and what does the triple dot triangle: "∴" mean? I understand every step except for the last one... thanks

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### Practice Exam.jpg
File size:
31.4 KB
Views:
110
2. Apr 11, 2013

### cepheid

Staff Emeritus

http://en.wikipedia.org/wiki/Divergence#Spherical_coordinates

To answer your second question, this symbol: $\therefore$ means, "therefore."

3. Apr 11, 2013

### bmb2009

ahh thank you so much