12.1.5	<0.7071||u||,0.7071||u||>
12.1.7	<cos(-20deg)||w||, sin(-20deg)||w||>
12.1.9	<-1,5>
12.1.11	<-2,-9>
12.1.15	<30,10>
12.1.21	2v=<4,6>, -w=<-4,-1>, 2v-w<0,5>, v+w=<6,4>
12.1.41	<3/5,4/5>
12.1.47	<cos(4pi/7), sin(4pi/7)>

12.2.11	P=<-2,-6,0>
12.2.13 a: parallel, same direction.
	b: not parallel nor has the same direction.
	c: parallel, but opposite direction.
	d: not parallel nor has the same direction.
12.2.25	not parallel
12.2.27	not parallel
12.2.31	<2/3,-2/3,-1/3>
12.2.49	r1(t) = <5,5,2> + t<0,-2,1>
	r2(t) = <5,5,2> + t<0,-4,2>
12.2.51	r1(t) = <4t-1, 2-2t, 2+t>
	r2(t) = <2t, 1, 1+t>
	when you set r1(t)=r2(t), you get
	<4t-1=2t, 2-2t=1, 2+t=1+t>, 
	which will result in 
	<t=1/2, t=1/2, 2!=1>.
	Since the z axis does not match, these functions will not intersect.