Atriangle has sides of length 5 ft, 9 ft, and 13 ft. what is the measure of the angle opposite the side that is 9 ft long? round to the nearest degree. 30° 41° 60° 87°

Using cosine theorem we have:
 9 ^ 2 = 5 ^ 2 + 13 ^ 2 -2 * 5 * 13 * cos (x)
 Clearing the angle we have:
 cos (x) = ((9 ^ 2) - (5 ^ 2) - (13 ^ 2)) / (- 2 * 5 * 13)
 cos (x) = 0.869230769
 x = acos (0.869230769)
 x = 29.63062742 degrees
 Round to the nearest degree:
 x = 30 degrees
 
 the measure of the angle opposite the side that is 9 ft long is:
 30 °