Need help breaking down how they get equation 5 using equations 1-4?

sin ( It - 0) sin 0' where u is given by Eqs. (1.6) and (1.7): D = VOM ( ven ' ). and using Eq. (1.8), we have: M De - VCM- 3 m Applying the law of cosines to the same triangle gives: 2 - 12 + VEM - 2VCMU' COS(1 - b), and combining the last three equations to express 0 as a function of o yields: tan 0 (M /m) sin o 1 + (M/m) cos