| Polygon |
Area formula |
Example |
Circle
|  |
A = R2 |
For a circle of radius 6 m.:
A = r2 =
3.14 x 36 = 113.04 sq. m.
|
| Triangle |
 |
A = B H / 2 |
B = 12 in. H = 4 in:
A = 12 x 4 = 24 sq. in.
2
Notice that you don't use the other side lengths!
|
| Trapezoid |
 |
A = (B1 + B2) H / 2 |
B1 = 9 cm. B2 = 16 cm.
H = 5 cm.
A = (9 + 16) x 5 / 2 = 62.5 sq. cm.
|
| Hexagon |
 |
A = 3 B H
|
where B is the length of one side and H is the distance from the middle of a side to the center of the hexagon (the apothem)
For a hexagon of base length 6 in and H = 4 in.:
A = 3 x 6 x 4 = 72 sq. in.
|
Any N-sided
regular polygon |
 |
A = N B H / 2 |
where N is the number of sides.
Think about it. This is just N little triangles whose bases are B and whose heights are H and whose apexes all meet at the center (like cutting a pie), so we have N triangles, each of whose area is
(B H / 2)
For this octagon, we have A = (8 x 6 x 4) / 2 = 96 sq. in.
|
