Two planes л₁ and л₂ have vector equations r.(5i-3j+k)=2 and r.(-i-9j+3k)=6 respectively. (a) Find the unit vector which is parallel to both planes. Hence, find a Cartesian equation for the line of intersection, I, of the two planes. (b) Find the angle between these two planes. (c) The planes л, has equation r.(-i+aj+bk)=6, where a and b are real numbers. Find the values of a and b given that the 3 planes л₁, л₂ and л, intersect in the common line l.​