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If x ,y ,a n dz are real and different a...

If `x ,y ,a n dz` are real and different and `u=x^2+4y^2+9z^2-6y z-3z x-2x y ,t h e nu` is always a. non-negative b. zero c. non-positive d. none of these

A

non-negative

B

non-positive

C

zero

D

none of these.

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