linear algebra
posted by Anonymous .
Solve for x if the vectors (2, x, 7x) and (x, 3, 2) are orthogonal

if orthogonal, then their dot product is zero
(2,x,7x) . (x , 3, 2) = 0
2x + 3x  14 + 2x = 0
7x = 14
x = 2
check:
(2,2,5).(2,3,2) = 4 + 6  10 = 0