if.....

Converting rads to degrees, we have

tan ( 60° -  A)  =  cot (60°)

And since they are co-functions....cot (60°)  =  tan(90° - 60°)  =  tan (30°)

So

tan (60 - A)  = cot(60)  = tan (30)

So

tan (60 - A)  - tan(30)

So   A  =  30°  =  pi / 6