A rectangle ABCD of dimensions r and 2r is folded along diagonal BD such that planes ABD and CBD are perpendicular to each other. Let the position of the vertex A remains unchanged and C1 is the new position of C. If ∠ABC1=θ, then cos θ is equal to

A rectangle ABCD of dimensions r and 2r is folded along diagonal BD su

1.	A rectangle ABCD of dimensions r and 2r is folded along diagonal BD such that planes ABD and CBD are perpendicular to each other. Let the position of the vertex A remains unchanged and C1 is the new position of C. If ∠ABC1=θ, then cos θ is equal to
Answer» A rectangle ABCD of dimensions r and 2r is folded along diagonal BD such that planes ABD and CBD are perpendicular to each other. Let the position of the vertex A remains unchanged and $C_{1}$ is the new position of C. If $∠ A B C_{1} = θ$ , then cos $θ$ is equal to