Problem $12$: For a given particle subjecting to the loads shown below, what is the good orientation of the coordinate system for writing equilibrium equations? F$1,$F$2,$ and F$3$ are parallel to each other and no force is perpendicular to other force.

Answer: $*$

$5$ points

$($a$)$ Selection of the coordinate system with the $x-$axis is along the horizontal direction.

$($b$)$ Selection of the coordinate system with the X$-$axis is along the direction of force F$1.$

$($c$)$ Selection of the coordinate system with the $x-$axis is along the direction of force F$5.$

$($d$)$ Selection of the coordinate system with the X$-$axis is along the direction of force F$6.$

$($e$)$ Selection of the coordinate system with the X$-$axis is along the direction of force F$7.$