**I) Vocabulary:**

**A) Midpoint**: A midpoint of a segment is the point that divides, or bisects, the segment into two congruent segments.

**B) Segment Bisector**: is a segment, ray, line, or plane that intersects a segment at its midpoint.

**Example:**Given segment AB bisects segment CD at point E. If CD = 10, what does AE and EB equal?

10/2 = 5 so they both equal 5 units.

**C) Angle Bisector**: is a ray that divides an angle into two adjacent angles that are congruent.

**Example:**Given angle PQR is bisected by ray QS, and measure of angle SQR = 22 degrees, what is the measure of angle PQR and angle PQS?

22 x 2 = 44 so measure of angle PQR = 44 degrees and when an angle is bisected, the two angles formed are congruent so angle SQR = angle PQS = 22 degrees.

**D) Midpoint Formula**: the mean, or average, of the x-coordinates and the y-coordinates.

therefore the midpoint formula is: ((x

_{1}+ x

_{2}) /2, (y

_{1}+ y

_{2}) /2)

**example:**Given A(-1, 7) and B(3, -3) what is their midpoint?

((-1 + 3)/2, (7 + -3)/2) = (2/2, 4/2) = (1, 2)