Any set of angles that form a line like A, B, and C add up
to 180 degrees.
Vertical angles – Opposite angles formed by
two intersecting lines like angle A and B below. Vertical angles have
equal measures.
2) Facts about triangles:
a) The three angles in a triangle add up to 180 degrees.
b) An equilateral triangle is a triangle with three equal
sides. The three angles of an equilateral triangle are all equal to 60
degrees.
c)
An isosceles triangle is a triangle with two equal angles.
The base angles opposite the equal sides are equal. In this case angles A
and B in the picture are equal.
d) A right triangle is a triangle that has a right angle.
The Pythagorean Theorem holds for all right triangles. It
says that:
Where 
and 
are
the two sides that make up the right angle and side 
is
the longest side of the triangle called the hypotenuse.
e) The height of a triangle is defined in terms of the base
of the triangle. Any side of the triangle can be chosen to be the base.
Once the base is chosen, the height of the triangle is the length of the
line segment drawn from the opposite vertex to the base such that it is
perpendicular to the base.
The examples above show the heights of 3 different triangles.
