Answer
(a) $ \vec A. \vec B = -2.736$
(b) $ \vec C. \vec D =-20 $
(c)$ \vec E. \vec F = 10.392$
Work Step by Step
(a) $ \vec A. \vec B = |A||B|cos\theta $
$ \vec A. \vec B = 2×4×cos(110 )$
$ \vec A. \vec B = 2×4×(-0.342)$
$ \vec A. \vec B = -2.736$
(b) $ \vec C. \vec D = |C||D|cos\theta $
Here $\vec C$ and $\vec D$ are in opposite directions so angle between them is 180 degree
$ \vec C. \vec D = 4×5×cos(180 )$
$ \vec C. \vec D = 4×5×(-1)$
$ \vec C. \vec D =-20 $
(c) $ \vec E. \vec F = |E||F|cos\theta $
$ \vec E. \vec F = 4×3×cos(30 )$
$ \vec E. \vec F = 4×3×0.866$
$ \vec E. \vec F = 10.392$
