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 |
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 |
×
= (
+2
+
) × (
+
+3
)
= 5 −
×
= (
−
+ 2
) × (−2
−
+
)
= −
−
cos =
=