What is the Well-Known Feedback Expression for Block Diagram Manipulation?

[Hraabo]

Hello I hope someone can help me, as i am kinda stuck for the moment.
As you can see, the assignment states that I need to find the poles from the closed loop transfer function.

I plan on doing so, by using block diagram reduction method.

This is as fare as I've come, and can't come further, even though I am pretty sure that it is possible. The summation point confuses me, how do I remove it? I could remove the feedback loop, but the summation point would still be there, or am I wrong?

Any help would be nice.

 

[anorlunda]

[Moved from a technical forum. No template.]

 

[LvW]

You must not "remove" the feedback loop but instead combine it with the forward block (2s).
This part of the system is nothing else than a local feedback loop which can be replaced by one single block (using the well-known feedback expressions).

 

[anorlunda]

using the well-known feedback expressions

@Hraabo , there is your hint. What well-known feedback expression did he mean?