So tana+tanb+tan (a+b) tanatanb = tan (a+b)

So Tan (60-a)+Tan (60+a)-√ 3 Tan (60-a) Tan (60+a).

= tan[(60-a)+(60+a)]= tan 120 =-√3

Extension: Generally, because this formula is a constant value, when a is arbitrary.

Can get its value, when a=0, the formula = √ 3+√ 3-3 √ 3 =-3, namely

The value of the formula is -√3.