If cos (A + B) sin (C - D) = cos (A - B) sin (C + D)
Show that: Â tan A tan B tan C + tan D = 0
cos (A + B) sin (C - D) = cos (A - B) Â sin (C + D)Â Â Â Â Â Â
Applying componendo and dividendo, we get       Â
     Â
 Â
            Â
      Â
 Â
Hence, Â Â Â