#### Answer

(a) $A\cdot B = -2.74$
(b) $C\cdot D = -20$
(c) $E\cdot F = 10.4$

#### Work Step by Step

(a) $A\cdot B = \vert {A}\vert ~\vert {B}\vert~cos(\theta)$
$A\cdot B = (2)(4)~cos(110^{\circ})$
$A\cdot B = -2.74$
(b) $C\cdot D = \vert {C}\vert ~\vert {D}\vert~cos(\theta)$
$C\cdot D = (4)(5)~cos(180^{\circ})$
$C\cdot D = -20$
(c) $E\cdot F = \vert {E}\vert ~\vert {F}\vert~cos(\theta)$
$E\cdot F = (4)(3)~cos(30^{\circ})$
$E\cdot F = 10.4$