Obtuse triangle
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An obtuse triangle is a triangle in which some angle is an obtuse angle. Any triangle which is not obtuse is either a right triangle or an acute triangle.
The obtuse triangles can also be defined in different ways:
- A triangle is obtuse if and only if two of its altitudes lie entirely outside the triangle.
- A triangle with sides of length
and 
, 
, is obtuse if and only if 
. This is known as the Pythagorean Inequality.
and 
, 
, is obtuse if and only if 
. This is known as the 
