Prove that `:(tan69^@+tan 66^@)/(1-tan 69^@tan66^@)=-1`

Prove that (tan69^@+tan66^@)/(1-tan69^@tan66^@)=-1 .

Prove that :(tan69^(@)+tan66^(@))/(1-tan69^(@)tan66^(@))=-1

Prove that (tan69^(@)+tan66^(@))/(1-tan69^(@)tan66^(@))=-1

Prove that : tan 69^@ + tan 66^@+ 1 = tan 69^@ tan 66^@ .

Prove that (i) "cos " 15^(@) - " sin " 15^(@) = (1)/(sqrt(2)) (ii) " cot " 105^(@) - " tan " 105^(@) =2sqrt(3) (iii) (tan 69^(@) + tan 66^(@))/(1-tan 69^(@) tan 66^(@)) =-1

Simplify be reducing to a single term : (tan 69^(@) + tan 66^(@))/(1 - tan 69^(@) tan 66 ^(@))

tan25^@=a prove that (tan155^@-tan115^@)/(1+tan155^@.tan115^@)=(1-a^2)/(2a)

Prove that tan6^@tan42^@tan66^@tan78^@=1

Prove that tan 12^@ tan 24^@ tan 48^@ tan 84^@ = 1 .

Prove that: tan10^(@) tan20^(@)tan70^(@)tan80^(@)=1