Question 1478
 Among 5,8 & 9 , the largest is 9 side. Let the angle opposite to the side 9 
 is A which is also the largest angle . By the cosine law:
 9^2 = 5^2 + 8^2  - 2*5*8 cos A = 25 + 64 - 80 cos A = 89 - 80 cos A
 So, cos A = 8/80 =1/10 > 0.
 Hence, A is acute and the triangle is acute.