You only need three formulas:
Area of a rectangle = length * width
Remember that a square is a rectangle for which length = width, so its area would be length^2.
Area of a circle = π * radius^2
The diameter of a circle is twice the radius, so radius = diameter/2, so the area can also be written as π * (diameter/2)^2
Area of a triangle = 1/2 * length * width
For a right triangle, the length and width correspond to the shortest two legs. For the non-right triangles shown here, the use the height of the triangle (dashed lines) and the bases that run perpendicular to them.
Some examples: (taken from the even-numbered pool)
2. The radius of the circle is 7 in, so the area is π * (7 in)^2 = 49π in^2.
6. This is a right triangle; its legs have lengths 15 mm and 20 mm, so its area is 1/2 * (15 mm) * (20 mm) = 150 mm^2.
8. The triangle has height 24 m and area 120 m^2. So the base has length b such that
120 = 1/2 * (24 m) * b
and solving gives b = 10 m.
12. The circle has area 200.96 cm^2, so the diameter d is such that
200.96 cm^2 = π * (d/2)^2
This gives (approximately, using π = 3.14)
64 cm^2 = (d/2)^2
8 cm = d/2
d = 16 cm
