=(sin(a+b)/cosacosb)((ctgactgb+1)/(ctgb-ctga)) - tgatgb=(ctgactgb+1)tgatgb-tgatgb=tgatgb(ctgactgb+1-1)=tgatgbctgactgb=1
=(sin(a+b)/cosacosb)((ctgactgb+1)/(ctgb-ctga)) - tgatgb=(ctgactgb+1)tgatgb-tgatgb=tgatgb(ctgactgb+1-1)=tgatgbctgactgb=1