Question

cos(A-B)/cos(A+B) +cos(C+D)/cos(C-D) = 0 then tanAtanBtanCtanD

Answer 1

COS(A-B) /COS(A+B)  +  COS(C+D)/COS(C-D) = 0

(COSACOSB + SINASINB ) / (COSACOSB - SINASINB)     +   
 
(COSCCOSD - SINCSIND) / (COSCCOSD + SINCSIND) = 0

1 + TANATANB / 1 - TANATANB     +   1 - TANCTAND / 1 + TANCTAND  = 0

1 + TANTANB + TANCTAND + TANATANBTANCTAND + 1 - TANCTAND - TANATANB + TANATANBTANCTAND = 0

2TANATANBTANCTAND + 2 = 0

TANA TANB TANC TAND = -1