Rhombus: Opposite sides parallel, ALL sides equal, opposite angles equal A rhombus is a
parallelogram in which all four sides are equal.
Rectangle: Opposite sides parallel, opposite sides equal, ALL angles 90° A rectangle is a
parallelogram with four right angles.
Square: Opposite sides parallel, ALL sides equal, ALL angles 90° A square is a type of
parallelogram, rhombus, and rectangle.
For any of these four shapes:
Area: A = bh, where b and h are perpendicular
Perimeter: P = the sum of all sides
Coordinate Geometry Formulas
All points are written (x,y), where x gives the x-coordinate and y gives the y-coordinate.
Two lines intersect when they meet at a single point.
Slope:
where (x 1 ,y 1 ) and (x 2 ,y 2 ) are two points on a line.
Slope-intercept formula: y = mx + b
where (x,y) is a point on the line, m is the slope, and b is the y-intercept, or the point at which the line
crosses the y-axis.
Use the slope-intercept form when a question asks for the slope of a perpendicular line. The slope of a
line perpendicular to it will be the opposite reciprocal or . That is, if slope of a line is 2, the slope of
a perpendicular will be −.
Parallel lines have equal slopes.
THE PROBLEMS
Plane Geometry
Let’s use these formulas and the Basic Approach to solve some problems.
