i am feeling very stupid. i have done 3 virtually identical rough-inclined-plane-friction questions and they are all wrong. mass 5kg on a rough inclined plane inclined at 30 degrees to the horizontal. is in limiting equilibrium. force F acting at 10 degrees from the parallel to the slope (vertically). so. resolving parallel to the slope, Xcos10-5gcos60=F F=(mu)R and mu=1/7 Xcos 10-5gcos60=1/7(5gcos30-xcos80) and solving for X i get X=30.3 the other 2 are the same kind of thing. is there something fundamental that i'm getting wrong??