The most general value of `theta` satisfying equations sin `theta` = `(-1)/2`, tan `theta` = `1/sqrt(3)` is
n`pi` + `pi/6`
2n`pi` + `(7 pi)/6`
2n`pi` + `(11 pi)/6`
n`pi` + (-1)n `(7 pi)/6`
it must be n'pi' + 'pi/6'