Question

PTG has side lengths of 18 cm, 27 cm, and 13 cm. which type of triangle is PTG? The answer is obtuse.

Answer 1

To know what kind of triangle is it. use the pythagorean theorem:
A^2 + B^2 = C^2,
where C is the longest side of the triangle 
if it satisfies the equation then it is a right triangle
if it does not then A^2 + B^2 > C^2 so it is acute triangle
if A^2 + B^2 < C^2 it is obtuse triangle

18^2 + 13^2 ? 27^2
324 + 169 ? 729
493 < 729 so it is obtuse triangle