Basic Geometry Concepts 
Coordinate Geometry 
Segment Addition Postulate 
The Distance Formula
The distance between the points A(x1, y1)
and B(x2,y2) is AB = square root
of (x2  x1)2 +
(y2y1)2. 
Unique Line Assumption 
The Midpoint Formula
The midpoint of the segment joining the points A(x1, y1)
and B(x2,y2)has the coordinates
[(x1 + x2)/2 [(y1 +
y2)/2]. 

The Slope Formula
The slope m of the line containing the points (x1, y1)
and (x2,y2) is m (y2 
y1) / (x2 x1). 

The equation of a line with slope m and yintercept b is y = mx +
b. 

Two nonvertical lines are parallel if and only if their slopes are
equal. 

Two nonvertical lines are perpendicular if and only if the product
of their slopes is 1. 

An equation of the circles with center (0,0) and radius r is x2
+ y2 = r2. 

An equation of the circle with center (h,k) and radius r is (x 
h)2 + (y  k)2 = r2. 

