Coplanar math problem

1. Apr 12, 2008

the.flea

1. The problem statement, all variables and given/known data
Find all values of t so that the three vectors a=(1,2,3) b=(4,5,6) and c=(7,8,t) are coplanar.

2. Relevant equations
(axb) $$\bullet$$ c=0

3. The attempt at a solution

(1, 2, 3) x (4, 5, 6)
(-3,6,-3)
(-3,6,-3)$$\bullet$$(7,8,t)
27=3t
t=9

it says find ALL values of t. i keep getting 9 through different combinations. is there only one value of t? thnks

Last edited: Apr 12, 2008
2. Apr 12, 2008

Dick

Yes, there is only one value of t. If you'd gotten 27=0*t for your last equation then any t would work. But you didn't.