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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

b.

cos−1

c.

cos−1

d.

cos−1



Question ID - 57212 | SaraNextGen Top Answer

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

b.

cos−1

c.

cos−1

d.

cos−1

1 Answer
127 votes
Answer Key / Explanation : (a) -

   ×  = (  +2  +  ) × (  +  +3  )

= 5  −     

 ×  = (  −  + 2  ) × (−2  −  +  )

=  −  −  

cos  =   =

127 votes


127