Let = = = λ (say). Since are mutually

perpendicular vectors, therefore = = = 0 ..............(i)

Now, = + + + + +

= | + + = 3 λ 2 [  = = = λ ]

∴ = ..............(ii)

Suppose makes angles θ 1 , θ 2 , θ 3 with and respectively. Then,

cos θ 1 = = =

= = = [Using (ii)] ⇒ θ 1 = cos –1

∴ Similarly, θ 2 = cos –1 and θ 3 = cos –1

Because θ 1 = θ 2 = θ 3 , so is equally inclineded with and

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