Question

The lengths of the sides of a triangle are 10​, 13​, and 19. classify the triangle as​ acute, right, or obtuse.

Answer 1

if c²=a²+b², it is a right triangle. 
if c²<a²+b², it is a acute triangle. 
if c²>a²+b², it is a obtuse triangle. 
in this case, 19²=361, 10²+13²=269. 19²>10²+13², so it is an obtuse triangle.