Assume symmetric reaction forces on both ends. So drawing the FBD of the complete chain. By vertical equilibrium we will have the vertical component of Reaction force at each end = W/2.
Tension (T) acts along the cable hence angle of the cable at the end would be the direction of the net reaction (R) which would be opposite to T. Now vertical component of R is W/2. Hence the horizontal component should be W/2 tan

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Considering the FBD of half the chain. By horizontal equilibrium we would have T= W/2tan

Also net reaction at the end R would be = W/2 sin
