I have two questions I need to make sure if I'm doing correctly. Its vectors. 1) For what values of a are the vectors i+3j-k and i+aj+k i) inclined at 30 degree angle cos@ = n1.n2 / |n1||n2| cos^2(30) * 11(2+a^2) = ((3a)^2) a=sqrt22 ii) perpendicular (1,3,-1).(1,a,1)=0 1+3a-1=0 a=0 2) Show that the lines r=s(i+2j+3k) r=(3i+5j+4k)+t(2i+3j+k) intersect I believe I should try and prove that they are not parallel. If their dot product is zero, then it means the lines are parallel. So if the answer is not zero, then I proved that the lines do intersect. Do I just take the cross product of (1,2,3) and (2,3,1)? I want to know if I'm using the correct vectors to do the dot product.