A bag of cement of weight $F_{k}$ hangs in equilibrium from three wires as shown in Figure $\mathrm{P} 5.20$ . Two of the wires make angles $\theta_{1}$ and $\theta_{2}$ with the horizontal. Assuming the system is in equilibrium, show that the tension in the left- hand wire is
$$
T_{1}=\frac{F_{k} \cos \theta_{2}}{\sin \left(\theta_{1}+\theta_{2}\right)}
$$