The exterior angle of a triangle is the angle that forms a linear pair with an interior angle of the the triangle. To draw the exterior angle all you need to do is to extend the side of the triangle. A linear pair is a pair of angle that forms a straight line. In the figure
Theorem. The sum of the interior angles of any triangle is 180°. Here are three proofs for the sum of angles of triangles. Proof 1 uses the fact that the alternate interior angles formed by a transversal with two parallel lines are congruent. Proof 2 uses the exterior angle theorem. Proof 3 uses the idea
The conditional probability of an event B is the probability that the event will happen given the knowledge that an event A has already happened. This probability is written P(B|A), notation for the probability of B given A. In the case where events A and B are independent, the conditional probability of event B given event A is simply the probability of event B, that is P(B). If events A and B are not independent, then the probability