Answer:
cosine
Step-by-step explanation:
c is the hypotenuse of the triangle and a is the adjacent side of the angle B.
On the other hand, the trigonometric functions sine, cosine, and tangent are equal to:
![\begin{gathered} \sin (Angle)=\frac{\text{Opposite Side}}{Hypotenuse} \\ \cos (\text{Angle)}=\frac{Adjacent\text{ Side}}{Hypotenuse} \\ \tan (\text{Angle)}=\frac{Opposite\text{ Side}}{Adjacent\text{ Side}} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/bmr7qvrui2oekg3tba8f7ermd0rx6v3o2d.png)
So, the trigonometric function that relates the angle B with its adjacent side a and the hypotenuse c is cosine.
Therefore, the answer is cosine.