Find u such that the vectors i + j - k, 2i - j + k and ui - j + uk are coplanar.

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- February 16th 2009, 01:56 PMbluebiroVector question.
Find u such that the vectors i + j - k, 2i - j + k and ui - j + uk are coplanar.

- February 16th 2009, 02:33 PMPlato
Solve for u.

- February 16th 2009, 03:25 PMHallsofIvy
Or: three vectors are co-planar if any one of them can be written as a linear combination of the other two.

Find a u such that a(i + j - k)+ b(2i - j + k)= ui - j + uk for**some**a and b. That is, a+ 2b= u, a- b= -1, -a+b= u. You can solve the first and second equations for a and u in terms of b, then find b so that the second equation is satisfied.