The edges of a rectangular parallelopiped are a, b, c; show that the angles between two of the four diagonals are given by cos − 1 
or cos − 1 
or cos − 1 
.
Text Solution
Verified by ExpertsA
Dr's of OP are a, b, c ; Dr's of AM are –a, b,c
If θ be the angle between OP and AM, we get 
= 
Similarly we can find the angle between other pairs and hence angles in general between six pairs are given by
Note : All +ve or -ve signs can not be taken because angle between diagonals are 0 or π radian is
not possible.
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