How do you prove tan^2(1/2theta)=(tantheta-sintheta)/(tantheta+sintheta)tan2(12θ)=tanθsinθtanθ+sinθ?

1 Answer
Oct 5, 2016

see below

Explanation:

tan^2(1/2 theta)=(tan theta-sin theta)/(tan theta + sin theta)tan2(12θ)=tanθsinθtanθ+sinθ

Right Side =(tan theta-sin theta)/(tan theta + sin theta)=tanθsinθtanθ+sinθ

=(sin theta / cos theta -sin theta)/(sin theta/cos theta + sin theta)=sinθcosθsinθsinθcosθ+sinθ

=((sin theta-sin theta cos theta) / cos theta) / ((sin theta+sin theta cos theta)/cos theta)=sinθsinθcosθcosθsinθ+sinθcosθcosθ

=(sin theta-sin theta cos theta) / cos theta * cos theta/(sin theta+sin theta cos theta)=sinθsinθcosθcosθcosθsinθ+sinθcosθ

=(sin theta-sin theta cos theta)/(sin theta+sin theta cos theta)=sinθsinθcosθsinθ+sinθcosθ

=(sin theta(1-cos theta))/(sin theta(1+cos theta))=sinθ(1cosθ)sinθ(1+cosθ)

=(1-cos theta)/(1+cos theta)=1cosθ1+cosθ

=(tan (1/2 theta))^2=(tan(12θ))2

=tan^2(1/2 theta)=tan2(12θ)

== Left Side