RIGHT TRIANGLES
The height is the perpendicular distance between the side that’s chosen as the base and the
opposite vertex.
In the triangle above, 4 is the height when 7 is chosen as the base.
82 . Triangle Inequality Theorem
The length of one side of a triangle must be greater than the difference between and less
than the sum of the lengths of the other two sides. For example, if it is given that the length of
one side is 3 and the length of another side is 7, then you know that the length of the third side
must be greater than 7 − 3 = 4 and less than 7 + 3 = 10.
83 . Isosceles and Equilateral Triangles
An isosceles triangle is a triangle that has two equal sides. Not only are two sides equal, but
the angles opposite the equal sides, called base angles, are also equal.
Equilateral triangles are triangles in which all three sides are equal. Since all the sides are
equal, all the angles are also equal. All three angles in an equilateral triangle measure 60
degrees, regardless of the lengths of the sides.
84 . Pythagorean Theorem
For all right triangles:
