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Find a unit vector with a positive first coordinate orthogonal to both 'a' and 'b' 
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#1
Sep2108, 12:08 AM

P: 3

hi! i'm new to the forums, and had a question that was more calculusrelated than physics. i saw another post similar to this one, but it was incomplete and i couldn't get the answer with the information on it, any chance someone could help me out?
The question is: "Find a unit vector with a positive first coordinate that's orthogonal to both 'a' and 'b' a=<1,8,1> b=<1,16,1>" the answer i got (which is only 1/3 right) was <1/8,0,1/8> i've tried using cross products, and then dividing by the magnitude of the cross product to get the unit vector, but only get the j variable right, and not i and k. i've also tried projecting a onto b (and visa versa) to find parallel vectors, and then trying the cross product again, but still can't seem to get the right answer. Any ideas? 


#2
Sep2108, 02:13 AM

Sci Advisor
HW Helper
P: 2,020

The vector you get is certainly orthogonal to both a and b, but it isn't a unit vector. This leads me to believe that you made some sort of mistake when you computed/divided by the magnitude of the cross product.



#3
Sep2108, 10:03 AM

P: 726




#4
Sep2108, 10:58 PM

P: 3

Find a unit vector with a positive first coordinate orthogonal to both 'a' and 'b'
you're both right, and i found the error. thank's a lot



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