Question 672462
We know that {{{3*tan^3(theta) = (3(3*sin(theta) - sin(3*theta)))/(3*cos(theta) + cos(3*theta))}}} 

So:

{{{(3(3*sin(theta) - sin(3*theta)))/(3*cos(theta) + cos(3*theta)) = tan(theta)}}}

Which for k being an integer we get:

{{{theta = pi * k}}}

{{{theta = (1/6)*(6*pi*k - pi)}}}

{{{theta = (1/6)*(6*pi*k + pi)}}}