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If x ,y and z are real and different and...

If `x ,y` and `z` are real and different and `u=x^2+4y^2+9z^2-6y z-3z x-2x y` ,then `u` is always (a). non-negative b. zero c. non-positive d. none of these

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CENGAGE PUBLICATION-COMPLEX NUMBERS AND QUADRATIC EQUATIONS-All Questions
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