1.

If q be the angle between the unit vectors a and b, then \[\cos \frac{\theta }{2}=\] [MP PET 1998; Pb. CET 2002]

A.             \[\frac{1}{2}\,|\mathbf{a}-\mathbf{b}|\]
B.             \[\frac{1}{2}\,|\mathbf{a}+\mathbf{b}|\]
C.             \[\frac{|\mathbf{a}-\mathbf{b}|}{|\mathbf{a}+\mathbf{b}|}\]
D.             \[\frac{|\mathbf{a}+\mathbf{b}|}{|\mathbf{a}-\mathbf{b}|}\]
Answer» C.             \[\frac{|\mathbf{a}-\mathbf{b}|}{|\mathbf{a}+\mathbf{b}|}\]


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