JEE Math Practice Question
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.cos$$-$$1$$\left( {{{17} \over {31}}} \right)$$
- B.cos$$-$$1$$\left( {{{9} \over {35}}} \right)$$
- C.cos$$-$$1$$\left( {{{19} \over {35}}} \right)$$
- D.cos$$-$$1$$\left( {{7 \over {31}}} \right)$$
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