Linear Dependence and Independence of Vectors

Q. If a, b, c are in G.P. and a^1/x = b^1/y = c^1/z, then xyz are in
(a) AP
(b) GP
(c) HP
(d) none of these

Q. The value of 'a' for which the vectors
A=2i-j-4k ,
B=i-5j+ak and
C=2i+3j+4k are linearly dependent is

Q. What is the difference between normal equation and parametric equation of parabola