geometry
posted by Matthew .
Classify the triangle as right, acute, or obtuse if the measures of its sides are 28, 46, and 53.

geometry 
MathMate
Use the cosine rule:
cos(A)=(b²+c²a²)/(2bc)
When a is the hypotenuse of a righttriangle, 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 righttriangle, acute or obtuse.
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