What is the derivative of $(cos x) / (1 + tan x)$ ?

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Answer 1 · 2015-05-15T21:44:32

I would use the Quotient Rule:
$y'=((-sinx(1+tanx))-(cosx(1/cos^2x)))/(1+tanx)^2=$
$=(-sinx-sinxtanx-secx)/(1+tanx)^2$

What is the derivative of (cos x) / (1 + tan x)(cos x) / (1 + tan x)?