Suppose \((l_1,m_1,n_1)\) and \((l_2,m_2,n_2)\) are the direction cosines of two lines and \(\theta\) is the angle between them such that
\[
\cos\theta=\pm(l_1l_2+m_1m_2+n_1n_2)
\]
Let \(A=(1,-2,3)\), \(B=(3,1,-3)\) and \(C=(-3,1,3)\) be the vertices of a triangle \(ABC\). Then \(\cos A=\)