\((1)\)若关于\(x\)的方程\(\dfrac{x+m}{x-3}+\dfrac{3m}{3-x}=3\)的解为正数,则\(m\)的取值范围是
\((2)\)在三角形纸片\(ABC\)中,\(∠\)\(C\)\(=90^{\circ}\),\(∠\)\(B\)\(=30^{\circ}\),点\(D\)\((\)不与\(B\),\(C\)重合\()\)是\(BC\)上任意一点,将此三角形纸片按下列方式折叠,若\(EF\)的长度为\(a\),则\(\triangle \)\(DEF\)的周长为 \((\)用含\(a\)的式子表示\()\)
\((3)\)一般地,当\(\alpha ,\beta \)为任何角时,\(\sin (\alpha +\beta )\)与\(\sin (\alpha -\beta )\)的值可以用下面的公式求得\(\sin (\alpha +\beta )=\sin \alpha \cos \beta +\cos \alpha \sin \beta \); \(\sin (\alpha -\beta )=\sin \alpha \cos \beta -\cos \alpha \sin \beta \)。
例如:\(\sin {{90}^{o}}=\sin ({{60}^{o}}+{{30}^{o}})=\sin {{60}^{o}}\cos {{30}^{o}}+\cos {{60}^{o}}\sin {{30}^{o}}=\dfrac{\sqrt{3}}{2}\times \dfrac{\sqrt{3}}{2}+\dfrac{1}{2}\times \dfrac{1}{2}=1\)。
类似地,可以求\(\sin {{75}^{o}}=\)
\((4)\)在平面直角坐标系中,直线\(l\):\(y\)\(=\)\(x\)\(-1\)与\(x\)轴交于点\(A\)\({\,\!}_{1}\),如图所示依次作正方形\(A\)\({\,\!}_{1}\)\(B\)\({\,\!}_{1}\)\(C\)\({\,\!}_{1}\)\(O\)、正方形\(A\)\({\,\!}_{2}\)\(B\)\({\,\!}_{2}\)\(C\)\({\,\!}_{2}\)\(C\)\({\,\!}_{1}\)、\(…\)、正方形\(A\)\({\,\!}_{n}\)\(B\)\({\,\!}_{n}\)\(C\)\({\,\!}_{n}\)\(C\)\({\,\!}_{n}\)\({\,\!}_{-1}\),使得点\(A\)\({\,\!}_{1}\)、\(A\)\({\,\!}_{2}\)、\(A\)\({\,\!}_{3}\)、\(…\)在直线\(l\)上,点\(C\)\({\,\!}_{1}\)、\(C\)\({\,\!}_{2}\)、\(C\)\({\,\!}_{3}\)、\(…\)在\(y\)轴正半轴上,则点\(B\)\({\,\!}_{n}\)的坐标是