Acute triangle—All three angles are less than 90 degrees, or the triangle has three
acute angles.
Obtuse triangle—There is one angle greater than 90 degrees, or the triangle has
one obtuse angle.
Equiangular triangle—An acute triangle in which all angles are congruent, or
when all three angles are equal.
Triangles can be further classified by their sides, as in the following:
Scalene triangle—There are no sides—and therefore no angles—that are equal;
in other words, no sides are congruent.
Isosceles triangle—Two of the sides are equal (congruent), and thus the base
angles are equal.
Equilateral triangle—When all three sides are equal (congruent).What are the partsof right and isosceles triangles?
There are special names for the parts of a right triangle. The hypotenuseis the side
opposite the 90 degree angle—the side that will always be the triangle’s longest. The
shorter sides are called the legs.
Similar to the right triangle, the isosceles triangle has specific names for its
182 angles and sides: Congruent (equal) sides are, as with the right triangle, called the
The basic types of triangles are acute (A), obtuse (B), right (C), scalene (D), isosceles (E), and equilateral (F).