已知向量\( \overset{→}{m} =( \sqrt{3} \)
\(\sin \)\( \dfrac{x}{4} \),\(1)\),\( \overset{→}{n} =( \)
\(\cos \)\( \dfrac{x}{4} \),
\(\cos \)\({\,\!}^{2} \dfrac{x}{4} )\),函数
\(f\)\(( \)
\(x\)\()= \overset{→}{m} · \overset{→}{n} \).
\((1)\)若\(f\)\((\)\(x\)\()=1\),求\(\cos \)\(( \dfrac{2π}{3} -\)\(x\)\()\)的值;
\((2)\)在\(\triangle ABC\)中,角\(A\),\(B\),\(C\)的对边分别是\(a\),\(b\),\(c\),且满足\(a\cos \)\(C+ \dfrac{1}{2} \)\(c\)\(=\)\(b\),求\(f\)\((B)\)的取值范围.