If we are talking on the force being exerted by a segment of a rope of lenght R on the right on a point M which is being also pulled from the Left by a segment of rope R as shown in the figure attached. Then we invoke Newton's Third Law:
"Any force exerted by an object (in this case a segment of the rope) also suffers a equal and opposite force".
If we pick [tex]T_R=T[/tex] whis is the tension exerted by the right segment then the left segment will also exert an equal and opposite force so we have that [tex]T_L=-T[/tex]
