Prove that -2? + j + 3k and 4? -2j -6k are parallel to each other.

If A and B are parallel, then the coefficients of  i , j, and k must be in proportion.

Since,   -2 / 4 = 1/-2 = 3/-6 = -1/2
the coefficients are in proportion => A and B are parallel to eache other.

Hence, proved.