A bearing$-$bearing intersection, based on user defined input of $2$ known stations and corresponding

bearings from those known stations,

$($a$)$ is always a double solution because two circles intersect in two places.

$($b$)$ can have no solution due to error in the input if the two lines $($bearings$)$ from the known points never

intersect.

$($c$)$ has two solutions as it requires the use of the inverse sine function.

$($d$)$ requires use of the law of cosines.