In the 8th grade Math Curriculum, we all learned Pythagoras' famous rule: If the square of the length of the longest side of a triangle is equal to the sum of the squares of the lengths of the other two sides then the triangle that was formed is right-angled. So, it should follow that: If the square of the length of the longest side of a triangle is less than the sum of the squares of the length of the other two sides then an acute triangle is formed. And: If the square of the length of the longest side of a triangle is greater than the sum of the squares of the lengths of the other two sides then an obtuse triangle is formed. Hope this helps!
