SHAPES AND FIGURES OF PLANE GEOMETRY Geometry Summary The important information in this chapter is summarized below. Shapes and Figures of Plane Geometry Summary Equilateral Triangle - all sides equal Isosceles Triangle - 2 equal sides and 2 equal angles Right Triangle - 1 angle equal to 90° Acute Triangle - each angle less than 90° Obtuse Triangle - 1 angle greater than 90° Scalene Triangle - each side a different length Area of a triangle - A = (1/2)(base)     (height) Perimeter of a triangle - P = side₁ + side₂ + side₃ Area of a parallelogram - A = (base)     (height) Perimeter of a parallelogram - P  =  2a  +  2b  where  a  and  b  are length of sides Area of a rectangle - A = (length)     (width) Perimeter of a rectangle - P = 2(length) + 2(width) Area of a square - A = edge² Perimeter of a square - P = 4 x edge Area of a circle - A = pr² Circumference of a circle - C = 2pr MA-03 Page 12 Rev. 0