Question

2sin(a/3)*ctg(a/3)-cos(a/3)=?

Answer 1

2sin(a/3)cot(a/3)-cos(a/3)=
2sin(a/3)*cos(a/3)/sin(a/3)- cos(a/3)=
2cos(a/3)-cos(a/3)=
cos(a/3)