Coeffiecient of friction question

[paneity]

[SOLVED] Coeffiecient of friction question

I'm probably being stupid here, but I just want to check I'm using the coefficient of friction right.

Homework Statement

A block on a plane, in equilibrium for the moment, the block has two ridges on the bottom, so reaction forces are split into R_{R}\ \mbox{and} \ R_{L} and the same for friction.

Is the coefficient of friction the whole of the frictional force on the block divided by the whole of the reaction force, of equal to the ratios of left and right forces?

i.e. \mu = \frac{F_{L}+F_{R}}{R_{L}+R_{R}}\ \mbox{or} \ \mu = \frac{F_{L}}{R_{L}} = \frac{F_{R}}{R_{R}}

I originally was certain that it was the latter, but if you could combine them like the former, it would make my impossible question quite simple.

 

[Shooting Star]

Both are the same. I hope you know enough elementary algebra to prove it.