Area and Perimeter of Plane Figures — Formula Sheet

Area = 1/2 × base × corresponding height (altitude) = 1/2 BC × AD

Area = √(s(s-a)(s-b)(s-c))

Perimeter = a+b+c = 2s

Equilateral triangle: Perimeter = 3a

Equilateral triangle: Area = (√3/4)a²

Area of quadrilateral = 1/2 × AC × (BX + DY)

Rectangle: Area = l × b

Rectangle: Perimeter = 2(l+b)

Rectangle: d = √(l²+b²)

Square: Area = a²

Square: Perimeter = 4a

Area of triangle = 1/2 × base × corresponding height.

Perimeter of a triangle = 2s.

Area = √(s(s-a)(s-b)(s-c)), where s = (a+b+c)/2.