Posted by Jake on .
For which value(s) of k will the dot product of the vectors (k,2k1, 3) and (k,5,4) be 7?
I did this so far,
2k1=5
6/2
k=3

Calculus 
Steve,
what's the problem?
(k,2k1,3)•(k,5,4) = k*k + (2k1)(5) + 3(4)
so, we need
k^2 + 10k  5  12 = 7
k^2 + 10k  24 = 0
(k2)(k+12) = 0
so, k=2 or 12
k=2: (2,3,3)•(2,5,4) = 4+1512 = 7
k=12: (12,25,3)•(12,5,4) = 14412512 = 7