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which type of triangle must have perpendicular lines
In a right triangle, two sides are always perpendicular. The measurements of these sides are used to calculate the area of a right triangle.
which type of triangle has obtuse sides
In an obtuse triangle, one angle is greater than a right angle—it is more than 90 degrees. An obtuse triangle may be isosceles or scalene.

Question: what is the difference
Self-contained rewrite: what is the difference between an isosceles and a scalene triangle