I try to solve a block diagram reduction example but when I did the operations, sign of one operation is incorrect. I tried to understand why it is so? Would somebody like to help me. (1) First I carry the feedback into the parallel line. (2) I add +1/G1H1 in the parallel line because I thought the orinal signal is that signal entering the parallel line. 3) I did serial and parallel operations but the result is incorrect by just a sign. T(s)=G3 +G1G2G3/1+G1H1 which is the correct answer. But the result I found by myself is T(s)=-G3+G1G2G3/1+G1H1 which is the wrong answer by a sign. Thank you.