\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(2i-j)=sqrt(10)*sqrt(5) CosA
CosA=5/5sqrt2= .707
solve for A
Use the law of cosines to find the angle of Q between the given vectors.
v=3i + j w=2i - j
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