Answer:
obtuse
Explanation:
a² + b² = c²
Let's use the two shorter sides as legs.
a² + b² = 31² + 54² = 961 + 2916 = 3877
c = √3877 = 62.2655...
For the triangle to be a right triangle, the third side would have to have a length of 62.2655. The actual length of the third side is 69. 69 is greater than 62.3, so the angle between the sides 31 and 54 must be greater than 90°. Therefore the triangle is an obtuse triangle.