For an acute angle $\theta$ of a right triangle, the cosine of $\theta$ is the ratio between the lengths of the adjacent side and the hypotenuse. The cosine of $\theta$ is written as $\cos \theta .$ While this trigonometric ratio expresses the ratio of the adjacent side to the hypotenuse, it does not state the actual measurements of their lengths. It should be noted that for a given angle, when the adjacent side and hypotenuse lengths change, if their ratio stays the same, then the cosine, too, would stay the same.