t g ω i = ( ctg β 1 i + ctg β 3 i ) − ( ctg β 2 i + ctg β 4 i ) ctg β 2 i ctg β 3 i − ctg β 1 i ctg β 4 i {\displaystyle \mathrm {tg} \omega _{i}={\frac {({\mbox{ctg}}\beta _{1i}+{\mbox{ctg}}\beta _{3i})-({\mbox{ctg}}\beta _{2i}+{\mbox{ctg}}\beta _{4i})}{{\mbox{ctg}}\beta _{2i}{\mbox{ctg}}\beta _{3i}-{\mbox{ctg}}\beta _{1i}{\mbox{ctg}}\beta _{4i}}}}