6. Let three non-collinear unit vectors $\boldsymbol{a}, \boldsymbol{b}, \boldsymbol{c}$ in the plane satisfy $\boldsymbol{a}+\boldsymbol{b}+\boldsymbol{c}=\mathbf{0}$. If $0 \leq t \leq 1$, then the range of $|-2 \boldsymbol{a}+t \boldsymbol{b}+(1-t) \boldsymbol{c}|$ is $\qquad$.
6. $\left[\frac{5}{2}, \sqrt{7}\right]$