Resolving along a plane involves breaking down forces into components that are parallel and perpendicular to the plane. In this case, the plane is the inclined pipe. To resolve forces along the plane, you will need to consider the weight of the pipe and the normal reaction force from the supporting pipes.
First, draw a free body diagram of the inclined pipe and label all the forces acting on it. This will include the weight of the pipe, the normal reaction force from the supporting pipe at a distance a, and the normal reaction force from the supporting pipe at a distance b.
Next, you will need to resolve these forces into components that are parallel and perpendicular to the inclined pipe. The weight of the pipe will have a component parallel to the plane, which will contribute to the force that is causing the pipe to slide down the plane. The normal reaction forces from the supporting pipes will also have components that are parallel and perpendicular to the plane. The perpendicular component of these forces will balance out the weight of the pipe, while the parallel component will contribute to the force that is keeping the pipe in place.
To find the distance that needs to be included in your equation, you will need to consider the distance between the point of application of the forces and the point where you are resolving the forces along the plane. For example, if you are resolving forces at the top of the pipe, then the distance between the point of application of the normal reaction force from the supporting pipe at a distance b and the top of the pipe will need to be included in your equation.
I hope this helps you understand how to resolve forces along a plane. It is important to carefully consider all the forces and their components in order to accurately solve the problem. If you are still having trouble, I would suggest seeking the guidance of a tutor or your instructor for further assistance. Good luck!