If y={1−tan x1+tan x},show that dydx=−2(1+sin 2x)
By the quotinet rule, we have,
dydx=(1+tan x),dydx(1−tan x).dydx.(1+tan x)(1+tan x)2
=(1−tan x)(−sec2 x)−(1−tan x)(sec2 x)(1+tan x)2 =−2sec2 x(1+tan x)2=−2(cos2 x)(1+tan2 x+2 tan x)
=−2(cos2 x){1+sin2 xcos2 x+2 sin xcos x}=−2(1+sin 2x)