The resultant of two velocity vectors `vec(A)` and `vec(B)` is perpendicular to `vec(A)`.

The resultant of two velocity vectors `vec(A)` and `vec(B)` is perpendicular to `vec(A)`. Magnitude of Resultant `vec(R )` is equal to half magnitude of `vec(B)`. If the angle between `vec(A)` and `vec(B)` is `(30 theta)^(@)`, then value of `theta` is ?