Homework question

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What am I doing wrong? Wouldn't you multiply the first vector by negative
one to find the opposite one?

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Last answer:
        AnSwEr0001: 6/sqrt(94)
        AnSwEr0002: -4/sqrt(94)
        AnSwEr0003: 7/sqrt(94)
        AnSwEr0004: -6/sqrt(94)
        AnSwEr0005: 4/sqrt(94)
        AnSwEr0006: -7/sqrt(94)
Number of correct attempts:   0
Number of incorrect attempts: 7
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Find two unit vectors orthogonal to a=<−1,1,2> and b=<-1,-5,4>.  Enter your answer so that the first non-zero coordinate of the first vector is positive.
First vector: < _ , _ , _ >
Second vector: < _ , _ , _ >
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Yes, you would multiply the first vector by -1 to get the second vector.  But to get a
unit vector orthogonal (perpendicular) to both a = ⟨−1,1,2⟩ and b = ⟨−1,−5−4⟩,  
you would start with  a x b, and then normalize to get a unit vector.  

You have computed a x b incorrectly (you can tell this because <6,-4,7> and <-1,1,2>
are not orthogonal since <6,-4,7>.<-1,1,2>√94 =(6*(-1)+(-4)*1+7*2)/√94=(-6-4+14)/√94
=4/√94≠0 ) and you have normalized incorrectly (since
 √(6^2+(-4)^2+7^2)=√(36+16+49) =√101≠√94).