hi shidubravin
Welcome to the forum.
(tan4A+tan2A)(1 - tan23A tan2A) = 2tan3A sec2A
Did you mean 23A here ? substituting A = 10 gives a LHS ≠ RHS.
please check your identity.
Also, you have posted in the exercises section => you are challenging us to find the solution you already know.
Did you want it in the help section => you want someone to help you to do the problem ?
Bob