Answer:
SOH-CAH-TOA (a)
Step-by-step explanation:
To find this question; Sohcahtoa is vital. Since you need to find cosine; the CAH is very important. This will tell you that it is adjacent over hypotenuse. In this case adjacent is 5 and the hypotenuse is ALWAYS the longest side on a triangle. So, that means the answer would be 5/13 or A. Hope this helps :)