Perimeter and Area of Plane Figures
Triangle
Let denotes the sides of the Triangle. Then: 

Rightangled Triangle
Let be the base, be the height (or perpendicular) and be the Hypotenuse. Then, 

Isosceles Right – angled triangle
Let the equal sides be . 

Equilateral Triangle
Let each of the side is . Then 

Isosceles Triangle
Let the equal sides be . Let the base be . Then 

Rectangle
Let the length and breadth . Then 

Square
Let the side of the square . Then 

Parallelogram
Let the two adjacent sides of the parallelogram be and 

Rhombus
A parallelogram that has all the sides equal is called a rhombus. If and are the diagonals, then 

Trapezium
A trapezium is a quadrilateral two of whose sides are parallel. A trapezium whose nonparallel sides are equal is known as an isosceles trapezium. Let and be the parallel sides and be the distance between the parallel sides. Then 

Quadrilateral
If and are the perpendicular distances from the diagonal of the quadrilateral from the vertices and respectively. Then, 