Area Formulae

a = length of side 1; b = length of side 2; c = length of side 3

Shape	Perimeter	Area
Triangle	a + b + c	base x 0.5 perpendicular height OR 0.5 ab Sin C OR SQRT of s x (s - a) x (s - b) x (s - c) where s = (a + b + c)/2
Quadrilateral	Sum of the sides	Sum of the areas of the two triangles caused by connecting two opposite corners.
Parallelogram	Sum of the sides	Base x perpendicular height
Trapezium	Sum of the sides	The perpendicular height x half the sum of the parallel sides.
Regular polygon	Sum of the sides	Half the sum of the sides x half the internal dia.
Hexagon	Sum of the sides OR 6 x a	2.5980765 x a² where a = length of side.
Octagon	Sum of the sides OR 8 x a	4.828427 x a²where a = length of side.
Circle	Pi x diameter	Pi x radius squared
Sector of circle	(2 x r) + d where d = (angle x r)/57.3	(Pi x angle x r)² / 360 OR Length or arc x half radius
Segment of a circle	(e2 + h2) / 2h where e = 2hr - h2 (or half of the flat side), h = height of the segment and r = radius of circle.	(Pi x r² x alpha) / 360 - e (r - h) where r = radius, alpha = angle subtended at the circle, e = half length of the flat side and h = height of the segment.
		As an approximation use 2/3 of the base x max height
Sphere		Surface area = 3.14159 x dia²

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