PreCal
posted by Hannah on .
Use the law of cosines to find the angle of Q between the given vectors.
v=3i + j w=2i  j

\vec b\cdot \vec c = \Vert \vec b\Vert\Vert\vec c\Vert\cos \theta
The law of cosines in vector form:
b dot c= abs b * abs c *CosA
(3i+j)dot(2ij)=sqrt(10)*sqrt(5) CosA
CosA=5/5sqrt2= .707
solve for A