There are 3 ways to describe a triangle when you are referring to the interior/inside of the shape. The key thing to remember is all triangles add up to 180 degrees. Once you remember that a triangle is a shape with 3 sides and 3 angles that add up to 180; you will note that 2 of the angles in every triangle will be less than 90 degrees. You will look to determine if the 3rd angle is exactly 90 degrees, more than 90 degrees, or if you notice that all 3 angles are less than 90 degrees.