If (tan x +sec x)(tan y + sec y)(tanz +sec z) = (sec x - tan x )(sec y - tan y ) (secz - tan z) = K, then the value of K is
±1
Divide and multiply
(tan x + sec x) (tan y + sec y)(tan z + sec z) to (sec x - tan x ) (sec y - tan y ) (sec z - tan z)
(secx−tanx)(secy−tany)(secz−tanz)×[(tanx+secx)(tany+secy)(tanz+secz)](tanx+secx)(tany+secy)(tanz+secz)
=1(tanx+secx)(tany+secy)(tanz+secz)
Suppose (tan x +sec x) (tan y +sec y) (tan z + sec z) =a
Then middle term becomes 1a
a=1a
a2=1a=±1
So, k=a=±1