Prove that the general solution of `costheta=cosalpha` is given by : `theta=2npi+-alpha,` where `n in Zdot`

Explanation

`costheta=cosalpha`
Using Identity
`cosA-cosB=-2sin((A+B)/2)sin((A-B)/2)`
`costheta-cosalpha=0`
`-2sin((theta+alpha)/2)sin((theta-alpha)/2)=0`
`sin((theta+alpha)/2)=0`
`((theta+alpha)/2)=npi`
`theta+alpha=2npi`
`theta=2npi-alpha`
`sin((theta-alpha)/2)=0`
`((theta-alpha)/2)=npi`
`theta-alpha=2npi`
`theta=2npi+alpha`
`theta=2npi pm alpha`