如图所示,角\(a\)的始边与\(x\)轴的非负半轴重合,终边与单位圆交于点\(A(x\)\({\,\!}_{1}\),\(y\)\({\,\!}_{1}\)\()\),将射线\(OA\)按逆时针方向旋转\(\dfrac{2\pi }{3}\)后与单位圆交于点\(B(x\)\({\,\!}_{2}\),\(y\)\({\,\!}_{2}\)\()\),\(f(a)=x\)\({\,\!}_{1}\)\(-x\)\({\,\!}_{2}\).
\((1)\)若角\(a\)为锐角,求\(f(a)\)的取值范围;
\((2)\)比较\(f(2)\)与\(f(3)\)的大小.