posted by Matthew .
Classify the triangle as right, acute, or obtuse if the measures of its sides are 28, 46, and 53.
Use the cosine rule:
When a is the hypotenuse of a right-triangle, cos(A)=0.
When a<90° cos(A)>0
When a>90° cos(A)<0
So by evaluating the cosine opposite the longest side, you can tell if the triangle is a right-triangle, acute or obtuse.