Note: tan(165)= tan(120+45)
tan(u+v)= [tex] \frac{tanu+tanv}{1-tanutanv} [/tex]
Substitute values:
tan(120+45)= [tex] \frac{tan120+tan45}{1-tan120tan45} [/tex]
tan(165) = [tex] \frac{ \sqrt{3}+1 }{1- \sqrt{3}(1) } [/tex]
tan(165)=[tex] \frac{ \sqrt{3}+1 }{1- \sqrt{3} } [/tex]
Rationalize (if needed):
[tex] (\frac{\sqrt{3}+1 }{1- \sqrt{3} } )( \frac{1+ \sqrt{3} }{1+ \sqrt{3} } ) [/tex]
=[tex] \frac{2 \sqrt{3}+4}{2} [/tex]
=[tex]- \sqrt{3}+2 [/tex]