1. The problem statement, all variables and given/known data If the vectors a and b are non-collinear and the vectors c = (x-2)a + b and d = ( 2x + 1)a - b , are collinear then x is equal to 2. Relevant equations c x d = |c| |d| sin θ n where n is unit vector 3. The attempt at a solution Since c and d are collinear there cross product magnitude would be zero. Also cross product of c and d is abx + 3ab Now | abx + 3ab | = 0 What would be | abx + 3ab | = ?