square = a 2 rectangle = ab parallelogram = bh trapezoid = h/2 (b1 + b2) circle = pi r 2 ellipse = pi r1 r2 triangle = (1/2) b h triangle given SAS = (1/2) a b sin C
triangle given a,b,c = regular polygon = (1/2) n sin(360°/n) S2
(pi
= 
= 3.141592...)
Areas
equilateral triangle = (1/4
(3) a 2
[s(s-a)(s-b)(s-c)] when s = (a+b+c)/2
(Heron's formula)
when n =
# of sides and S = length from center to a corner
Information supplied by http://www.math2.org