A tetrahedron has vertices P (1, 2, 1), Q (2, 1, 3), R (-1, 1, 2) and O (0, 0, 0). The angle between the faces OPQ and PQR is

\(co{s^{ - 1}}{\rm{}}\left( {\frac{17}{{31}}} \right)\)

\(co{s^{ - 1}}{\rm{}}\left( {\frac{7}{{31}}} \right)\)

\(co{s^{ - 1}}{\rm{}}\left( {\frac{9}{{35}}} \right)\)

\(co{s^{ - 1}}{\rm{}}\left( {\frac{19}{{35}}} \right)\)

A tetrahedron has vertices P (1, 2, 1), Q (2, 1, 3), R (-1, 1, 2) an

1.	A tetrahedron has vertices P (1, 2, 1), Q (2, 1, 3), R (-1, 1, 2) and O (0, 0, 0). The angle between the faces OPQ and PQR is
A.	\(co{s^{ - 1}}{\rm{}}\left( {\frac{7}{{31}}} \right)\)
B.	\(co{s^{ - 1}}{\rm{}}\left( {\frac{9}{{35}}} \right)\)
C.	\(co{s^{ - 1}}{\rm{}}\left( {\frac{19}{{35}}} \right)\)
D.	\(co{s^{ - 1}}{\rm{}}\left( {\frac{17}{{31}}} \right)\)
Answer» D. \(co{s^{ - 1}}{\rm{}}\left( {\frac{17}{{31}}} \right)\)