If \(3\) vectors \(\overline{a},\overline{b},\overline{c}\) are such that \(\overline{a}\neq \overline{0}\) and \(\overline{a}\times \overline{b}=2(\overline{a}\times \overline{c})\), \(|\overline{a}|=1\), \(|\overline{c}|=1\), \(|\overline{b}|=4\), and angle between \(\overline{b}\) and \(\overline{c}\) is \(\cos^{-1}\left(\dfrac{1}{4}\right)\) and \(\overline{b}-2\overline{c}=\lambda \overline{a}\), then \(\lambda=\)