Key Formulas of Plane Geometry

　　Pythagorean Theorema2 + b2 = c2, where a and b are the lengths of the legs of a right triangle, and c is the length of the hypotenuse.　　Area of a TriangleArea = bh, where b is the length of the base and h is height.　　Sum of the Interior Angles of a PolygonThe sum of the interior angles of a polygon is (n – 2)180°, where n is the number of sides in the polygon.　　Area of a TrapezoidArea =　h, where s1 and s2 are the lengths of the bases of the trapezoid, and h is the height.　　Area of a Parallelogram, Rectangle, and RhombusArea = bh, where b is the length of the base, and h is the height.　　Area of a SquareArea = s2, where s is the length of a side of the square.　　Circumference of a CircleCircumference = 2πr, where r is the radius of the circle.　　Arc LengthArc Length =　 2πr, where n is the measure of the degree of the arc, and r is the radius of the circle.　　Area of a CircleArea = πr2, where r is the radius of the circle.　　Area of a SectorArea of Sector =　 πr2, where n is the measure of the central angle which forms the boundary of the sector, and r is the radius of the circle.