Figure 3-10. Sides and altitude
c. The general types of triangles are shown in Figure 3-11. They are as follows:
(1) An acute triangle has interior angles that are less than right angles.
(2) A right triangle has one right angle and two acute angles.
(3) An obtuse triangle has one obtuse angle and two acute angles.
(4) An isosceles triangle has two equal sides and two equal angles.
(5) An equilateral triangle has three equal sides and three equal angles and is sometimes
called an equiangular triangle. All of the angles within an equilateral triangle are less than right angles;
therefore the equilateral triangle is also an acute triangle.
d. Obtuse and acute triangles are often called oblique triangles to distinguish them from right
triangles. Triangles with three unequal sides are called scalene triangles.
Figure 3-11. Types of triangles
EN0591
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