4.
设等差数列\(\{a_{n}\}\)满足:\(\cos ^{2}a_{3}\cos ^{2}a_{5}-\sin ^{2}a_{3}\sin ^{2}a_{5}-\cos 2a_{3}=\sin (a_{1}+a_{7})\),\(a_{4}\neq \dfrac {kπ}{2}\),\(k∈Z\)且公差\(d∈(-1,0)\),若当且仅当\(n=8\)时,数列\(\{a_{n}\}\)的前\(n\)项和\(S_{n}\)取得最大值,则首项\(a_{1}\)的取值范围是\((\) \()\)