# Ques. -13

**Geometry**Level 4

Let \(\vec{a},\vec{b},\vec{c}\) be non-zero vectors such that no two are collinear and \((\vec{a} \times \vec{b}) \times \vec{c}=\frac{1}{3} \cdot |\vec{b}| \cdot |\vec{c}| \cdot \vec{a}\). If \(\theta\) is the acute angle between the vectors \(\vec{b} \ and \ \vec{c}\), then \(sin\theta\) is equal to :