A person standing on the bank of a river observes that the angle of elevation of the top of a tree on the opposite bank of the river is 60o and when he retires 40 meters away from the tree the angle of elevation becomes 30o. The breadth of the river is
20 m
30 m
40 m
40 m
The cosine of the angle between any two diagonals of a cube is
A.
Let the direction ratio's of two diagonals of a cube are
(1, 1, 1) and (- 1, 1, 1).
=
=