Question

Prove that tan inverse 1/4+tan inverse2/9=1/2cos invers3/5

Answer 1

given 3 tan a tanb=1

so, tan a tanb =1/3

change them in sin and cos

now sina sinb /cos a cos b=1/3

apply componendo and dividendo

use the forluae for cos(a+b) and cos (a-b). you will get your answer.

Answer 2

given 3 tan a tanb=1

so, tan a tanb =1/3

change them in sin and cos

now sina sinb /cos a cos b=1/3

apply componendo and dividendo

use the forluae for cos(a+b) and cos (a-b). you will get your answer