Find a unit vector with a positive first coordinate orthogonal to both 'a' and 'b'


by samazing18
Tags: coordinate, orthogonal, positive, unit, vector
samazing18
samazing18 is offline
#1
Sep21-08, 12:08 AM
P: 3
hi! i'm new to the forums, and had a question that was more calculus-related 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?
Phys.Org News Partner Science news on Phys.org
Going nuts? Turkey looks to pistachios to heat new eco-city
Space-tested fluid flow concept advances infectious disease diagnoses
SpaceX launches supplies to space station (Update)
morphism
morphism is offline
#2
Sep21-08, 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.
JG89
JG89 is offline
#3
Sep21-08, 10:03 AM
P: 724
Quote Quote by morphism View Post
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.
I second this. I didn't do the work myself, but dividing the components of the vector by the magnitude of the vector is the correct method to use so you probably did make a mistake in your calculations.

samazing18
samazing18 is offline
#4
Sep21-08, 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


Register to reply

Related Discussions
How to find vector coordinates in non-orthogonal systems? Linear & Abstract Algebra 13
Find the Unit Vector Calculus 3
Forming an orthogonal matrix whose 1st column is a given unit vector Calculus & Beyond Homework 3
Closed curve and orthogonal curvilinear coordinate system Calculus 9
orthogonal projection, orthonormal basis, coordinate vector of the polynomial? Linear & Abstract Algebra 1