Answer
$$1$$
Work Step by Step
Since the trigonometric function $\cos$ is an even function, we can write
$f(-\theta)=f(\theta) \implies \cos ({-40^\circ})=\cos (40^\circ)$.
Therefore, $\dfrac{\cos (-40^\circ)}{\cos (40^\circ) }=\dfrac{\cos (40^\circ)}{\cos (40^\circ) } \\=1$
