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.