Divergence of gravitational field in Gauss's law

[bmb2009]

Homework Statement

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

Homework Equations

The Attempt at a Solution

 

[cepheid]

Homework Statement

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

Homework Equations

The Attempt at a Solution

To answer your first question:

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


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

 

[bmb2009]

ahh thank you so much