Question

How do you solve `tan(x+ y) = (tan x + tan y) / (1 - tan x tan y)`?

Answer 1

It is a trignometrical identity, there is nothing there to solve. The identity is arrived at by simplifying the identities in `sin(x+y)/cos(x+y)`

= `(sinx cosy +cosx siny)/(cosx cosy -sinxsiny)`.

Divide the numerator as well as the denominator by cos x cosy to get

`(tanx +tany)/(1-tanx tany)`