How tan(π/4-θ) = (1−tanθ)/(1+tanθ) ?

Derivation of

tan(π/4-θ) = (1−tanθ)/(1+tanθ)

As, tan(π/4+θ) = (1+tanθ)/(1-tanθ)

...........👉👉Derivation of tan(π/4+θ) = (1+tanθ)/(1-tanθ)

{Put θ= -θ}

tan(π/4-θ) =

[1 + tan(-θ)] /[1- tan(-θ)]

        { As tan(-θ) = -tanθ }

Hence,

tan(π/4-θ) = (1-tanθ)/(1+tanθ)