The cosine of the angle A of the triangle with vertices $A(1,-1,2), B(6,11,2),C(1,2,6)$ is

Question

$$\begin {array} {1 1} (a)\;\frac{63}{65} & \quad (b)\;\frac{36}{65} \\ (c)\;\frac{16}{65} & \quad (d)\;\frac{13}{64} \end {array}$$